exaSound s88 multichannel D/A processor

I have reported on exaSound DACs since the introduction of the e18 in 2013, but those reports were in my Music in the Round column. This is Stereophile's first full review of an exaSound product and the first time one has spent time on JA's test bench.

ExaSound offered the first multichannel DAC that was intended for serious audiophiles and music lovers. I bought the e28 and have continued to use exaSound multichannel DACs. I use them just as much for stereo as for multichannel; stereo recordings still constitute about half my library.

For stereo-only audiophiles, exaSound has made stereo DACs with each generation, starting with the e12. The company's stereo DACs feature the same technology found in the multichannel versions, differing mainly in channel count.

The time is ripe for a thorough look at an exaSound DAC because, while exaSound DACs have continued to evolve, the s88 ($6500) is something new. It has integrated networking technologies that eliminate the need for additional boxes and cables and expand its useful operation. The s88 offers standard RCA outputs as well as full-size XLR connections instead of the annoying mini-XLRs from previous multichannel models. The technical specs in the Specifications—see sidebar—are impressive.

The s88 Streaming DAC is one of four new products from exaSound, each with a different feature set. There's a multichannel DAC, the e68, which lacks the s88's streaming features, balanced outputs, and volume control. (There are some circuit differences as well.) There is also a two-channel DAC, the e62 (footnote 1), which lacks streaming features and the volume control but includes balanced outputs. The Delta Music Server (see review) completes the quartet.

The s88 retains the distinctive, proprietary features of previous models, including a true asynchronous USB interface with error correction, which exaSound calls "ZeroJitter"; a unique volume control with four-way volume synchronization for convenience and dynamic range ("ZeroResolutionLoss"); galvanic isolation for external noise reduction ("GalvanicInfinity"); Quad-clock architecture with an 82 femtosecond master clock and three auxiliary stream-control clocks ("FemtoMaster"); and true balanced circuits.

Several of the s88's features are especially worth remarking on. The volume can be set from the front panel, the remote control, or any source component (ie, server) that can run exaSound's device drivers. And the s88's superb galvanic isolation has proven itself in this respect: When used with the s88, whether attached by USB or S/PDIF, some very high-quality and expensive servers have been unable to provide any audible improvement, or anyway, none that I could hear.

Because of the s88's larger size (compared to previous exaSound DACs), there now are autonomous balanced and unbalanced output stages for each channel so that all outputs can be used simultaneously with less electromagnetic interference and interchannel crosstalk. The bigger chassis also allows for future upgrades of the output stages, streamer CPU, RAM, and SSD storage.

The most important new feature is integrated streaming, which is more powerful than that in most of the add-on devices it renders unnecessary. The s88 supports lossless streaming (wired or wireless) via Roon RAAT, Signalyst (HQPlayer) NAA, and OpenHome/UPnP as well as hard-wired inputs via TosLink, S/PDIF, and USB. In addition to its familiar (and superb) Windows ASIO driver (footnote 2), exaSound provides a MacOS "High-Performance" driver for Mac's Core Audio that supports PCM up to 32/384 and DSD over PCM (DoP) up to DSD256. Alternatively, their proprietary Mac ASIO driver (for the moment, only for Roon) bypasses Core Audio and supports native DSD up to DSD512. That covers essentially all stereo or multichannel formats in general commercial use, even those from specialty audiophile labels.


Unpacking and Setup
The s88 fills out a full-width chassis, its front panel featuring a crisp, clear display. To the left of the display is the power button and a ¼" headphone jack; to the right are three buttons—for IR RC setup, input selection, and mute—plus the volume knob: In an all-digital system, the s88 can supplant the preamplifier. The up/down pushbuttons on previous exaSound DACs were ergonomically inadequate, forcing the use of an Apple Remote (wherever did I put it?), which was included. I immediately took to the volume knob—convenient and smooth—although I did wish the knob was bigger and had more inertia.


Around back, on the top left, are connectors for two Wi-Fi antennas. Below that is a recessed panel with several more connectors; the essential things here are the main (DC) power connection and the RJ-45 (Ethernet) streaming connector. Also on the recessed panel are two HDMI connectors—one for viewing a user interface (UI) on a monitor, the other reserved for future use—and two USB 2.0 connectors, which allow you to connect a keyboard and mouse for navigating that UI. Two USB 3.0 connectors are provided for connecting locally stored music.

On the right of the back panel are the DAC's analog outputs (eight of them, each with XLR and RCA connectors). Next to those are the standard digital inputs—USB-A, TosLink, RCA S/PDIF—plus a DC toggle switch for selecting the power supply configuration, a reset button, a 12V trigger connection, and a place to connect a second DC power supply.

Why two power-supply connections? You can run the s88 with just the one—an offboard switching supply is supplied—or you can connect a second, third-party supply to power the DAC, while the original PS serves only the streaming module. I used the split-power arrangement, with secondary linear power provided by a TeddyPardo Teddy12/2.

I set up the s88 by connecting the other end of the included PS to the AudioQuest Niagara 5000 and an Ethernet cable from the RJ-45 jack to my local LAN switch. (Later, I also connected the Pardo power supply.) I also connected the USB "B" input to, alternately, exaSound's Delta Server and my newly updated Baetis Prodigy server. The balanced (XLR) outputs were connected to my power amps via a Coleman eight-channel (analog) switch. The output voltage of the s88 was sufficient to drive the Benchmark AHB2 amps to quite satisfying levels even when the amps were set to their middle input-sensitivity setting.

The listening experience
When I powered up the s88 and selected the Ethernet input, both servers saw the s88 as Roon RAAT outputs, and I could play to the s88 from either one. JRiver (on the Baetis) also saw the s88 and played to it via UPnP. Interestingly, each server could interrupt the other with a new request, causing the current source to pause. Very orderly. This made A/B comparisons easy, and it allows other streamers you might have around the house to put their two cents in when desired. New requests via LAN also superseded playback from S/PDIF and TosLink—but not USB.

Footnote 1: In more detail, the e62 uses ES9028pro and supports MQA while the eE68 uses ES9038pro and no MQA. In addition, the headphone amplifier of the e62 can handle twice the output current compared to the e68. The analog output stages are different. The power lines for the DAC chips and the analog output stages are different.

Footnote 2: exaSound provides no drivers or support for Linux.

exaSound Audio Design
3219 Yonge St., Suite 354
Toronto, Ontario
Canada M4N 3S1

JRT's picture

The article states, "...it was little more than a tick from the main speakers and a bip from the subs. I only heard it from the unbalanced inputs—it was absent when I hooked things up with RCA."

Kal, I suspect that you had intended the word "balanced" rather than "unbalanced" in this, if the problem went away on the RCA terminated interconnection.

Kal Rubinson's picture

Thanks. Actually, it really should say "I only heard it from the balanced outputs—it was absent when I hooked things up with RCA."

John Atkinson's picture
Kal Rubinson wrote:
Actually, it really should say "I only heard it from the balanced outputs . . .


John Atkinson
Technical Editor, Stereophile

JRT's picture

...keeping the audio interface separate from the separately replaceable and upgradable computer and software.

Kal Rubinson's picture

I prefer the idea of having the multiple input options on the s88 without additional boxes and cables.

myro99's picture

Hi Kal,
I'm looking to make a major upgrade to my current multichannel DAC (Oppo 205). For 5.1 SACD music (harder to convert / download to files), would it make sense to use the Oppo 205 as a transport and send the files digitally to the Exasound from the Oppo? I plan to start burning multichannel DVD-A's and Blu-Rays to a NAS down the road but want to know if the Oppo digitally into the Exasound will produce strong results on par with feeding the Exasound with NAS files. I've learned not to assume anything. Thanks, Gary

Kal Rubinson's picture

For 5.1 SACD music (harder to convert / download to files), would it make sense to use the Oppo 205 as a transport and send the files digitally to the Exasound from the Oppo?

I do not see how that is possible. The only MCH outputs from the Oppo are HDMI or analog and the exaSound will not accept either.