Note: for the full suite of measurements from the SoundStage! Audio-Electronics Lab, click here.

Since its inception in 2005, the NAD Masters Series range has been populated with the company’s finest audio components at relatively reasonable prices. The latest amplifiers in the series all utilize Purifi Audio’s Eigentakt technology and are widely considered some of the best performing amps for the price. The new Masters M66 streaming preamplifier is designed to complement NAD’s top-of-the-line stereo power amplifier, the M23, in both aesthetics and performance. It offers a scope of features rarely seen in this type of component at any price.

So what do you get for the M66’s $5499 price (all prices in USD)? In addition to a high-performance DAC with a separate analog preamplifier section, you also get the BluOS multiroom streaming platform, Dirac Live Full Frequency room correction, and Dirac Live Bass Control for up to four independent subwoofers. Not to mention a high-quality MM/MC phono stage, a headphone output, and pretty much every other feature you could ask for in a streaming preamplifier.

Streaming features and future-proofing

Utilizing the BluOS multiroom streaming platform developed by sister company Bluesound, the NAD Masters M66 has an extensive set of streaming features, similar to that of other BluOS-enabled products, such as the NAD Masters M33 and the Bluesound Node X.

BluOS supports over 20 streaming services, including Amazon Music, Deezer, iHeartRadio, Napster, Neil Young Archives, nugs.net, Qobuz, SiriusXM, Spotify, and Tidal. It also supports Tidal Connect, Spotify Connect, and Apple AirPlay 2, and it is compatible with Amazon Alexa and Apple Siri voice control. Networking is available via Wi-Fi or ethernet, and Bluetooth connectivity includes the AAC, LDAC, and aptX HD codecs. It is compatible with smart-home control systems such as Crestron, Control4, ELAN, RTI, and URC. For those who prefer to use Roon over BluOS or any other music-management software, the M66 is Roon Ready.

On the hardware side of things, the M66 incorporates ESS Technology’s flagship Sabre ES9038PRO DAC and ES9822PRO ADC chips and a high-performance i.MX8 digital processor. The preamplifier section consists of an ultraprecise, IC-controlled stepped resistor ladder, a design used in many modern high-end preamplifiers. The digital and analog sections are physically shielded from one another by a large plate interposed in between, and each has its own power supply.

The M66 supports NAD’s latest Modular Design Construction2 (MDC2) technology with two expansion slots for MDC2 modules. The MDC2 standard includes two-way communication between the module and the host component, which allows great flexibility in upgrade options. The new MDC2 BluOS-D module, for instance, augments the component with Dirac Live room correction and BluOS multi-room streaming. (The M66 has both capabilities natively, but the MDC2-compatible C 3050, C 399, and C 389 integrated amplifiers don’t.) Components compatible with the MDC2 standard no longer support the original MCD modules; and while the BluOS‑D is the only MDC2 module available currently, more are sure to come: NAD has a long history of future-proofing their products with the original MDC modules.

Case and connections

NAD Masters components have been class-leading in build quality and aesthetics, and the M66 is no exception. In industrial design it is unmistakably a Masters Series component: a brushed-aluminum case with a contrasting matte-black faceplate and top panel; a large, black volume knob on the right; an illuminated NAD logo that changes color to indicate power status on the left; a flush-mounted capacitive power button atop the front panel. In fact, in its overall size and seven-inch touchscreen display, the M66 is identical to the M33 streaming amplifier. It measures 5.3″H × 17.1″W × 15.2″D, standing on spiked feet over magnetically attached metal discs, and weighs 16.7 pounds.

The back panel is brimming with inputs and outputs. As expected, multiple digital inputs are available: two RCA coaxial and two TosLink optical, one AES/EBU on XLR, an HDMI eARC port, for connection to a television, and a USB-A port, for connection to local storage. An ethernet port allows wired LAN connection. There are also connectors for the supplied Bluetooth and Wi-Fi antennas. Line-level analog inputs include one pair of balanced (XLR) jacks and two pairs of single-ended (RCA) jacks as well as two pairs of phono inputs (one for MM, one for MC) and their associated grounding post. Two pairs of analog outputs are provided: one single-ended, one balanced. Two sets of four subwoofer outputs are provided too: one set single-ended, the other balanced.

Additional connections are an RS-232 control port, a 12V trigger input and two outputs, a micro-USB service port, and a standard IEC power inlet with a mains power switch. Two unoccupied, covered MDC2 slots are found on the left side of the panel for future expansion/upgrades, as mentioned.

The M66 does not have a USB-B port for connection to a computer, and it is not compatible with DSD, but a future USB-B MDC2 module that supports DSD might already be in the works. (A first-generation MDC module with this capability is available for compatible components.) In the meantime, BluOS does offer the option of transcoding and storing DSD files as FLAC files, which the M66 supports. It also supports WAV and AIFF files as well as full MQA decoding and rendering. Be mindful, however, that BluOS is limited to a maximum resolution of 24-bit/192kHz. The M66 does not offer home-theater bypass, but that could conceivably be implemented in a future upgrade.

As mentioned, along with BluOS, one of the better streaming platforms currently available, the M66 includes licenses for Dirac Live Full Bandwidth, arguably the premier room-correction system, and Dirac Live Bass Control (Multi Subwoofer). These two killer apps, if purchased on their own, would cost you $349 and $549, respectively.

Included with the M66 is NAD’s stout and solid SRM1 remote control. The SRM1 offers access to only basic BluOS functionality, but most users will likely use the BluOS Controller app from a personal computer or mobile device to take advantage of the full functionality of BluOS.

The M66 carries a relatively short two-year warranty.

Setup

I did most of my listening with the M66 feeding a pair of NAD M23 power amps ($3749 each) in bridged mode. The NAD components replaced the Anthem STR preamplifier ($4299.99) and pair of Anthem M1 monoblock amplifiers ($3999.99 each) that I normally use in my system to drive a pair of MartinLogan Masterpiece Classic ESL 9 hybrid electrostatic loudspeakers ($7499.98/pair) and a pair of JL Audio E-Sub e112 powered subwoofers ($2700 each). The rest of the system consisted of my usual assortment of components and accessories: an Intel NUC computer streaming Tidal and locally stored audio files via Roon, a Pro-Ject X1 turntable with a Pick it S2 MM cartridge, and cables and power products from Shunyata Research, Analysis Plus, Clarus, ESP, Zero Surge and Blue Circle Audio.

With the Anthem STR, I use Roon almost exclusively; with the M66, however, I used BluOS for the most part. I ran the Windows, Android and macOS versions of BluOS in this audition, and all worked well. When I did use Roon, I encountered no issues. Tidal Connect raised none either.

For the first couple of weeks, by way of a break-in period, I had the M66 in my second system, connected to my home network by an ethernet cable. The BluOS app immediately recognized it, and I was up and running within a matter of minutes. I then moved the M66 into my main system, connected it wirelessly to the network, and configured the Dirac Live software. This took a bit of time, but it was relatively straightforward. NAD supplies a measurement microphone with the M66, together with a generic calibration file. I chose to use my Dayton Audio UMM-6 measurement mike instead as it comes with its own, unit-specific, calibration file.

Taking advantage of Dirac Live’s ability to store multiple filters, I measured the M66 with both the NAD M23 and Anthem M1 amplifiers. Then, switching back and forth between the two filters in BluOS, I was better able to pick out differences in the M66’s performance with these two amplifiers.

NAD, on its “Dirac” web page, makes available for download a Dirac Live target curve, developed by PSB’s Paul Barton. It is quite similar to the target curves of Harman’s ARCOS and Anthem’s ARC room-correction systems. At times, with certain tracks, I wished this target curve yielded a little more bass. I attempted to adjust the curve to compensate for this—Dirac Live allows endless tweaking of target curves—but this sometimes led to excessive bass on other tracks. I ended up settling on the NAD target curve in its original state.

While the M66 is an extremely high-quality streaming preamplifier, Dirac Live, in optimizing the sound of the system for the acoustic space it’s in and seamlessly integrating the subwoofers with it, consistently and noticeably improved its performance. I therefore left it engaged at all times.

Musical attractions along route M66

When I listen to Eigentakt-based amplifiers, such as the NAD M23 or the recently reviewed Lyngdorf MXA-8400, since their sound is so neutral and transparent, I always get the sense that I am hearing every last detail in a recording. Not surprisingly, this is exactly how I felt when I listened to the M66 streaming preamplifier.

On the intricately recorded orchestral composition “Raiders March (From Indiana Jones and the Raiders of the Lost Ark),” from John Williams: The Berlin Concert (24-bit/192kHz FLAC, Deutsche Grammophon / Tidal), the pulsing notes of brass, strings, and timpani were imaged precisely on a broad soundstage, imparting a sense of the expanse of the physical stage at the Berliner Philharmonie concert hall, where this recording was made. The strikes of the timpani lingered ever so slightly but were still taut and drawn with precision. The cymbals, barely audible, still rose clearly from the horns in the background. This was followed by the sharp snap and staccato of the snare, which contrasted with the more fluid sound of the timpani. The presentation wasn’t as spacious as in the terrific Dolby Atmos Blu-ray version of this recording, but owing to the M66’s transparency, it was still wide and deep.

Less complex multitrack recordings, such as the Fine Young Cannibals’ cover of Elvis’s “Suspicious Minds (Caught in a Dub),” from the remastered and expanded 1985 release of the band’s eponymous album (24/44.1 FLAC, London Music Stream / Tidal), sounded surgically clean. The softly wavering synth notes, dryly recorded drums, and vocals—all hung in midair in the space in front of me. This is one of several excellent remixes of the song on this album. “Suspicious Minds (Suspicious Mix)” is more of a rock’n’roll version; “Suspicious Mind (Shakedown Mix)” is a melancholy, mostly vocal mix. The M66 exposed the subtle differences in sound between these different versions and let me fully appreciate their uniqueness.

My pressing of Fleetwood Mac: Greatest Hits (Warner 081227959357) is not exactly the quietest piece of vinyl I own. With the M66, however, surface noise on this record was noticeably lower than it usually is. The voices of Christine McVie and Stevie Nicks sounded extremely clean and clearly separate from the instrumental accompaniment, as did Lindsey Buckingham’s voice (though it sounded somewhat recessed on “Tusk”).

One of my customary reference vinyl tracks, the title song from Bruce Springsteen’s Tunnel of Love (Columbia 88985460131), is another less-than-perfect-sounding LP. With the M66, I felt I was hearing this record at its very best. Sibilance was tamed enough not to be distracting but not so much as to soften Springsteen’s voice and render it indistinct. The sound was always clean, never harsh, and was imbued with satisfying weight and substance.

I’ve auditioned some fantastic sounding integrated amplifiers over the years that had excellent phono stages—the Yamaha A-S3200 ($7999.95) and Technics SU-R1000 ($9999), for instance—that made my $999 Pro-Ject X1 turntable with its Pick it S2 MM cartridge sound like a much more expensive and accomplished deck. Such was the case with the M66. But when processed by Dirac Live and Bass Control and mated to the neutral and powerful M1s or M23s, it made vinyl sound especially appealing in my system.

And if that weren’t enough, the M66 also has an outstanding headphone output. It didn’t sound quite as full-bodied and powerful as my JDS Labs Atom headphone amplifier ($99) and Apple USB-C dongle ($9), my reference desktop system, but it came pretty close when driving a pair of HiFiMan HE400se headphones. Compared to the headphone output of my Oppo UDP-205 Blu-ray Disc player, vocals were notably more detailed and distinct, and therefore more intelligible, but still smooth and highly musical.

The Anthem STR challenge

By any measure, the M66 is a richly featured, first-rate preamplifier; but it wasn’t until I compared it directly to the Anthem STR that I fully appreciated all that it has to offer. The STR has provided state-of-the-art integration and room correction for my ML ESL 9s and JLA e112 powered subwoofers for many years. Back in 2020, Diego Estan reviewed the STR on SoundStage! Access and Doug Schneider wrote an opinion piece about it on SoundStage Hi-Fi. They both raved about the Anthem’s broad feature set, especially its flexible bass management and ARC Genesis room-correction system. Diego pronounced the STR extraordinary for its price; Doug took it further, calling it extraordinary regardless of its price. Now, the M66 offers a more sophisticated room-correction system, one based on Dirac Live and Bass Control, as well as a fully featured, multiroom streaming platform with wireless capability, something the STR lacks.

With the Anthem STR, the 2024 remastered and expanded version of Erasure’s Cowboy (24/44.1 FLAC, BMG / Tidal) was utterly captivating in its stark EDM sound that was spread widely between the speakers. On the cover of Blondie’s “Rapture,” the opening synth scales hovered nimbly, weightlessly, between the speakers, while the tight, throbbing beat provided a solid base to which the song remained anchored throughout.

With the NAD M66, the background was quieter by comparison, which further expanded the soundstage and increased the space between the instruments and Andy Bell’s vocals. The M66 brought more of his voice to the fore and rendered it with greater clarity. This was most noticeable during the creatively distorted rapping portion of the lyrics.

The subterranean bass on “Full of Life,” from Paranoïa, Angels, True Love (24/176.4 FLAC, Because Music Tidal), by Christine and the Queens, was deeper and better articulated with the M66 than with the STR. When the track’s deep, long tones started to pound, they filled up my listening room and held fast, with no discernible overhang.

On its Dirac Live Bass Control web page, Dirac states that “Bass Control leverages all-pass filters, plus machine learning and artificial intelligence, to calculate gains, delays, and all-pass filters for each subwoofer.” Anthem’s ARC Genesis room-correction system allows automatic adjustment of subwoofer phase to optimize it for the main speakers, but it relies on a much older DSP chip and is more limited in what it can do. One feature the STR does have that the M66 doesn’t is home-theater bypass mode, which in the STR includes the subwoofers—they are always in the circuit, whether in multichannel playback or stereo. In my combined stereo-HT system, I have found this invaluable. I know of no other component that offers such flexibility in an HT-bypass mode.

Conclusion

There is nothing groundbreaking about any one thing that the NAD Masters M66 does. Its DAC, ADC, and phono sections are all high quality, as is its analog volume control. But they are in many other streaming preamps too. It employs Dirac Live and Bass Control as well as the BluOS streaming platform, which are also found in other streaming preamps. What is remarkable about the M66 is that it brings these and a wealth of other great features together in one well-designed, excellent sounding, and attractively styled and priced component. With all that it offers, I would not hesitate recommending the NAD M66 if it cost $10,000. At its price of $5499, it’s a no-brainer. I cannot think of another product at a comparable price that comes close to the M66 in performance and flexibility, let alone one that surpasses it and is more deserving of my recommendation.

I urge you to consider auditioning the M66, particularly if your stereo system includes high-quality subwoofers. If it doesn’t, adding subwoofers and the M66 is worth considering too. In my system, whether paired with the Anthem M1s or the NAD M23s, the M66’s control was exemplary, and its performance was stellar.

. . . Roger Kanno
rogerk@soundstagenetwork.com

Note: for the full suite of measurements from the SoundStage! Audio-Electronics Lab, click here.

Associated Equipment

• Speakers: MartinLogan Masterpiece Classic ESL 9
• Subwoofers: JL Audio E-Sub e112 (x2)
• Preamplifier: Anthem STR
• Power amplifiers: Anthem M1 (x2 monoblocks), NAD Masters M23 (x2 in bridged mode)
• Digital sources: Intel NUC computer running Windows 11, Roon, and Tidal; AudioQuest JitterBug jitter reducer
• Turntable: Pro-Ject Audio Systems X1 turntable with Pick it S2 cartridge
• Speaker cables: Analysis Plus Blue Oval, Shunyata Research Venom-X
• XLR interconnects: Shunyata Research Venom-X, Analysis Plus Silver Apex
• USB link: Analysis Plus Purple Plus
• Power cords: Clarus Cable Aqua, Essential Sound Products MusicCord-Pro ES
• Power conditioners: Blue Circle Audio PLC Thingee FX-2 with X0e low-frequency filter module, Zero Surge 1MOD15WI

NAD Masters M66 streaming preamplifier
Price: $5499
Warranty: Two years, parts and labor

NAD Electronics International
633 Granite Court
Pickering, Ontario L1W 3K1
Canada
Phone: (905) 831-6555
Fax: (905) 837-6357

Website: www.nadelectronics.com