@CraftyClown
Thank you! I've added your results to the third post.
Both players' responses look pretty good actually. You can try it yourself, differences below 1 dB are really not that easy to spot, especially without quick A/B comparisons. 0.5 dB differences are even harder to spot and everything below is almost impossible. On good days, I am able to get a 0.3 dB difference (quick A/B-ing) with good concentration (it is still mostly a game of guessing then), but usually everything below 1 dB is not easy (well, that's an understatement) to spot without quick direct comparisons, especially if they don't take part in the midrange where our hearing is the most sensitive.
It's best to take that as a general rule (the case might be different if one is extremely used to one in-ear/headphone and very fine-grained digital volume control, but even then everything around 0.5 dB is not easy to guess at all and requires hard concentration, a quiet environment and a fresh mind).
Having said that, also the channel "imbalance" in post #98 is negligible and not even necessarily addressable to the DAP output but could also be caused by the cable, socket or when the computer is busy doing other things at the same time (e.g. streaming videos or caching websites when the browser is open). And even if it is, it's still below 0.2 dB and much less than what many fully analogue volume pots show in terms of imbalance.