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Before deciding to attempt this mod I looked for other people's impressions on its effect and there doesn't seem to be more than a handful of posts and comments out there, and quite conflicting by the way. So for those looking for the same thing I'm adding my experience.

First, my initial impression of the unmodified amp compared to that of the RME ADI-2. I thought it sounds more different than better. It has noticeably more punch and it's a little bit more detailed. At the same time, all these punch and detail is covered by a slighly dark fog, not enough to make it sound unappealing but still noticeable. The ADI-2 is extremely detailed to begin with but I noticed that with the Singxer a lot of small details in songs give me the impression that there's something going on near me in the room rather tham coming from the headphones, which doesn't happen with the ADI-2. I feel I could listen to any of these amps without missing the other one (only that one option is considerably more expensive and bulkier..)The Singxer has more punch but it's darker while the ADI-2 is more vibrant and crispier.

As for the mod, the first thing I did was to measure the DC component of the ADI-2's balanced outputs: I measured 9mV while playing a 1kHz sine wave at 0db, 3mV at -10dB and 1mV when no sound was being played. So I figured it was safe to do the mod.

I didn't have any PC jumpers (I swear I had some somewhere) and in Amazon they come in 200 units for €11. I wasn't going to buy 200 jumpers to use only four but I do have a bunch of flag terminals that have the same size but the grip was too loose, so I squeezed the holes with a pair of small pliers and that did the trick.

After putting everything back together I measured the DC component of the outputs to make sure it was safe to plug my headphones. The voltages (left and right) where 4.7/3.9 mV for the SE output and 1.40/0.12 mV for the balanced one. Still safe.

I started with the HD560S just as one more paranoid precaution to check that they wouldn't blow up, they didn't so I moved to the Aryas. Wow! The difference was evident, the dark fog is now completely gone, the punch that was already better than the ADI-2 became even better with a far more detailed attack on the bass and kickdrum. The upper range is where the increase in detail is more evident: a shy tambourine in the background for example now sounds more evident. The amp in the ADI-2 is SOTA already so there's no detail that you could miss but my subjective impression is that with the modded Singxer those details are there without you concentrating on noticing them while with the ADI-2 you only notice things when you look for them.

In conclusion, my advice for owners of an RME ADI-2 is that the upgrade is not worth it unless you're willing to do the mod. The Singxer is maybe 5% better than the ADI-2's amp but with the mod is where it really starts to shine. It's hard to recommend an amp that requires you to void the warranty to make it sound at its best but I did quite a lot of research before buying it and couldn't find a better option in this price range. The next logical step would be the Soloist 3xp since anything in between wouldn't be worth it over stretching the budget to the Soloist.

Lastly, one important warning: unscrew only the six torx T8 screws! The larger ones fix the board to the base and unscrewing them will make the whole board loose, held only by the plugs and switches. Also, when you flip the amp after removing the screws, mind that the cover is only the top, the sides are part of the bottom.

Thanks for reading if you made it this far and I hope you found this post useful. Will gladly answer any questions you have about the amp or the mod.