I respect the genuine effort to do this properly. Methodologically there was one error, however. You may not have changed the volume control, but the output voltage of the two units may have been different. Mind you, I am not saying that this is what made the difference, but methodologically it does matter.
Substantively the take home is, of course, that a great effort was needed to maybe, but only maybe, establish a tiny difference.
Not according to the output voltage specs of the *three* components used (Yggy, ERC-3, UDP-205). But I respect your (good) point.
Look, I admit, I do not run or have access to a "scientifically exactly perfect audio laboratory".
For purposes of what I was trying to achieve, accomplish, etc. I’ll stand pat on my decision that in my case the Yggy was and is the correct purchase, and that my testing is *more than* satisfactory.
EDIT:
I agree differences in digital can be tiny and hard to discern. But it’s worth the effort (IMO) once you realize, understand and can prove with reasonable certainty that the component change was/is worthwhile. I wouldn’t go back to delta-sigma from multi-bit R2R. No way. *BIG* difference. (with the Yggy that is. My assumption is that multi-bit implementation will best delta-sigma in any case). More "authentic sounding", period.