I picked up one of these units on a recent trip to the UK. That was largely motivated by a desire to see what Pro-Ject were able to ring out of the ESS 9038 vs. some of the other, much more expensive, options that have been trickling in from China. That it is a dual-converter design, has MQA support (a point of interest/experimentation for me, even if I remain extremely skeptical about it), a feature-list that belies its diminutive size, and comes in just under $400, made it more interesting still.
The thing is tiny, for sure. Small enough that I could almost see throwing it in with my primary laptop when I am not trying to travel light. It easily bests the performance of the AudioQuest Dragonfly Red or Meridian Explorer 2 that I tended to use for that role.
The headphone output seems suitably transparent, if a bit anemic (though totally reasonable for the size/price/target market of the unit) ... not something I'd pair with anything demanding. With this in mind I first gave it a try using the ATH-M50x, a pairing that sits very well and is unexpectedly enjoyable. I wound up listening to the thing all-day in that configuration without fatigue or issue. Surprising given my normal TOTL setup and a generally more miss-than-hit set of experiences with ESS based units.
Pairing with (stock), 2016-era, HD650 was very agreeable (and plenty loud). Even feeding the Focal Utopia (directly) things remained enjoyable - and while probably not a typical, nor ideal, combination, I didn't see a good reason not to try them - nor did I find any obvious issues while doing so.
Different filters options bring about, for the most part, audible differences, though sometimes they're very subtle.
It is a nice touch on a unit at this level to have multiple options to power it. It sounds very good just fed both signal and power off a single USB connection. Performance improves in a reasonably-easy-to-audibly-discern manner/level by using the included outboard PSU. I also tried the unit with external iFi Power and Teddy Pardo power-supplies and, in both cases, I was only able to tell the difference when using the unit as a DAC feeding my "proper" amp and into my HD800S, Abyss and Utopia cans. Using the built-in headphone output, PSUs other than the included one did not exhibit a difference I could detect.
Other thoughts ...
On pre 2.12 firmwares, there were some irritating issues with the unit with mixed DSD samples rates and mixed DSD/PCM playlists. Pops and clicks being the principal issue. This is a very common thing with a lot of DSD-capable units (feed even a Chord DAVE via USB and this happens here and there). These seem to have been eliminated in v2.12.
I have experienced no other issues with DSD playback.
Even on v2.12, however, with MQA content, fed from Audirvana+ and sourced via TIDAL, there are, sadly, still some drop-out issues. The situation is improved, but not fixed completely. An MQA track will be playing, and then suddenly the volume will drop noticeably, the MQA indicator will go out, and a few moments later the MQA light comes back on, the volume comes back up, and all is normal. It's annoying, but not frequent ... sometimes you could go several albums without this happening. And it's definitely improved from earlier firmwares, though there's still a little way to go here.
It is worth saying that this MQA dropout issue has NEVER occurred using the Meridian Explorer 2, and that's from the same sources and chain (the only difference being the USB cable, but I'm 100% sure that's unrelated).
Presentation is neutral and detailed (without the exaggerated "sharpening" of detail I've heard on much more expensive ESS units).
The MQA support is that of a full decoder, rather than the software-assisted renderer model of, say, the iFi Nano iDSD BL. MQA content, via TIDAL, remains a bit of an enigma. Some albums sound better compared to the CD-rips I own ... but it's impossible to tell if this is down to the MQA version simply using a better/different master vs. it actually being anything to do with the technicalities of MQA itself. Though, if all MQA got me was access to better masters in some cases, that would be interesting in and of itself, and doesn't necessarily need an MQA-capable DAC to take advantage of.
I expected to be underwhelmed by the "Pre Box S2 Digital" ... instead I think this is actually a rather worthy unit. Value is very high. Performance is solid. I like it quite a bit better than a couple of either higher-profile or oddly-hyped, more expensive units based on the same basic chipset.
If you don't need/want DSD or MQA support, and don't mind using a couple of boxes instead of one, and/or have more demanding cans, I think the Schiit Modi MB/Magni 3 offer a somewhat better overall result, with better drive-capability and dynamics. And the iFi Micro iDSD BL will yield more power, more control, work better with demanding cans, but with no (current) MQA support (if you care), and a somewhat more engaging presentation (for me) ... though the iFi has channel balance issues that were an issue with more sensitive full-size cans (e.g. Fostex TH-X00 PH ... which were otherwise a lovely combination).
YMMV
