I have recently bought a Gustard X26 Pro, after having owned a D90 for a while (and falling for the hype of "it's as good as it gets and the measurements are there to back it up") and after a short romance with the Denafrips Ares II. Neither of the DACs was what I had hoped to get, but each of them had strengths where the other's weaknesses lay, so for a few months I kept them both to switch between depending on the genre of music I was listening to.
The D90 was very clear and crisp-sounding, also quite punchy, incisive and direct. But it also sounded quite two-dimensional, what I would call "a high-resolution facsimile of sound". Good for electronic music but quite unconvincing (dry, flat) for everything else.
The Ares II was almost the opposite - not so high-res (even in the OS mode, the OS Slow being my favourite one), far "wispier" and less punchy, but much more holographic, more 3D-sounding, warmer and richer.
After a few months, the switching was driving me crazy as at the end of the day neither of the DACs was giving me what I was after and instead of enjoying music (like I used to in the beginning), each of them served as a reminder of the other's strenghts.
So, after some research I decided that unless I was going for sometething crazy-expensive (which I was not) like a Dave + Mscaler or Holo Audio May + HQ Player, my best options, if were to sell both the D90 and the Ares II, would be to either buy a Gustard X26 Pro or a Pontus II. I went with the former because having heard the Ares II I was not 100% convinced if R2R was for me (at least the way Denafrips do it - not true NOS, still oversampled and in either of the OS modes basically being a lower-res version of a chipset-based DAC without an output stage, hence I believe the holography). I also didn't like the idea of buying a DAC (Pontus) which by definition is far from the best the company has to offer.
My goodness, this is by far the best DAC I've ever heard! It's exactly what I had hoped for and more. It's the best of the D90 and the Ares II and then some. It retrieves even more details than the D90 but does it in such a wonderful way where everything is holographic, three-dimensional, each sound has its own space (not just left to right but also in terms of depth) and however busy a song gets, things never get congested. In terms of detail retrieval, it makes the background sounds of the D90 sound hazy in comparison (!). I think it's partly due to there being so much more depth, making each sound appear as being surrounded by its own "air" - a hologram as opposed to being painted on a two-dimensional canvas, if that makes sense. It doesn't have the "warmness" of the Ares II, but to be fair I didn't really like it as such, it was colouration and the only good thing about it was that it seemed to have got rid of all sharpness. But the Gustard doesn't have any sharpness in the treble, either, and it does it without colouring the sound. It also brings the body back to music (compared to the D90, but also the Ares II to some extent) where sounds no longer feel empty/hollow - there's depth and almost physicality to them.
In other words - music is music again, each song has its own atmosphere/soul which is allowed to shine through seemingly without any limitations. The D90 made everything sound more or less the same (as if the sound was flattened so as to come out roughly the same, almost metallic I would say), the Ares II got rid of the sharpness at the price of having less detail, sounding warmer, much less dynamic, albeit more holographic (the aforementioned lack of output stage - I think Gustard has achieved this by using only discrete components, hence retaining the same holography that I loved in the Ares II, but without any impedance issues that the Ares II has). The Gustard has it all and the diference on my system can be jaw-dropping (Focal Utopia, Hifiman HE1000se).
I wholeheartedly recommend this DAC to everyone whose system is resolving enough to show differences between DACs. I'm certain that there will be people out there who, like me, focused on getting the right headphones first (which is probably the right thing to do) and are stuck with something like the D90, wondering if it's worth upgrading without going all the way up to those ridiculously expensive devices (which I have not heard). This one has been a gamechanger for me, the most important purchase I have made since the headphones themselves. I can finally stop analysing music or wishing that X or Y was better - this one has it all and I would risk saying that anything above it will not be better as such, just different (e.g. R2R for those who find it more natural-sounding). It's also got a NOS mode (not real NOS, as I understand it, but it at least allows to bypass internal oversampling) which makes it possible to use Roon's oversampling or HQPlayer (I have tried Roon and it is a little different indeed, but I find Gustard's own doing a better overall job).
I hope that this post helps someone find their audio nirvana like I have found mine with the Gustard.
***Update Jan 2023***
As much as I've loved the Gustard since day one, there is a way to make it sound better... much better... to the point that I'm thinking this surely must be close to as good as it gets.
The way to do this is to override the DAC's internal oversampling. I don't believe that the full modulation etc. can be overriden (one would probably need a DAC like the Holo Audio May for that) but the results I have been getting are nothing short of spectacular. In order to do this, the DAC needs to be put in the "NOS" mode and the incoming signal needs to be upsampled by external software. I have been using Roon + HQPlayer. My journey has been as folows:
- Roon's upsampling - airier, more separated sound than Gustard's stock tuning, however - less body. Overall a nice change but I felt that I was sacrificing one area slightly in order to get gains in another. I got hooked, though, to the point of no longer using Gustard's internal oversampling.
- HQPlayer (PCM) - HQPlayer is a game changer. I first experimented with PCM, the elsewhere-recommended Sinc-M and Sinc-L filters (apparently closely resembling what the MScaler does). Sinc-M sounded meaty and tactile, but not airy enough for me. Sinc-L sounded like Roon's upsampling on steroids with the body back. I thought my journey was over until I tried the settings recommended by the developer of the HQPlayer...
- HQPlayer (DSD) - ... namely filters called poly-sinc-gauss-long and poly-sinc-gauss-hires-lp with PCM being converted to DSD. This is the biggest jump in audio quality I have experienced since buying the Gus X26 Pro which I thought was already good enough! Two things seem to be happening here - firstly, the different filters, as per the HQPlayer's manual, are much better at reconstructing depth. In comparison, the stock Gus sounds like the D90 sounded to me when I got the Gus. The change is very obvious and changes the musical experience. Secondly (bear in mind my technical knowledge is limited), either the PCM to DSD conversion changes something (which I don't think it should if it's done right, if anything it adds noise which then needs to be filtered out at very high sampling rates) or, more likely, it allows the DAC to better process the incoming signal (1 bit vs 16 bits). My understanding is that the HQPlayer does the PCM to DSD conversion much better than the DAC would have processed the bits internally, hence making things even easier for the DAC in terms of there being even less processing left for the DAC to do internally (or, put more bluntly, fewer opportunities for the limited processing power of the DAC to mess things up/oversimply things).
The results on my gear (Utopia and HEKse, but actually mostly the former, the extra depth results in the HEKse struggling to keep up now!) are spectacular. The conversion to DSD creates even more depth and the kind of separation that I've previously heard
@GoldenOne describe in relation to R2R DACs as instruments having a very specific placement within the soundstage (as opposed to sounding hazy or "floating"). To a small degree I experienced that when I had the Ares II but what I'm hearing now is way better than that. And things despite being just as detailed as before are smoother. Whether it's better reconstruction of transients or simply the fact that the depth results in sounds not being so close to/on top of each other ("wall of sound") - I'm not sure, but the overall effect is sound that is so much more life-like and as such engaging, immersive and addictive (in a good way).
I'm certain that the results will vary depending on what headphones one uses (Utopias are known for their depth) but if you are a Gus X26 Pro owner you owe it to yourself to try the above, especially since HQPlayer can be downloaded for free (with a 30-minutes-per-session time limit)! All I wanted from the software was to get what I was getting from Roon's upsampling but with more body and I ended up getting something that truly transformed my already-very-good DAC into the best musical experience I've ever had.