First of all, my point is, you don't always need volume matching, of course if you want to exclude all margin of error, but as an example do you need volume matching to hear that 2 car engines sound completly different? I don't think so. It's obvious.
I am not a fan of head-fi, i am not in to forum rivalries either, i generally dislike forums tbh, because somehow forums are like cults, little variances of opinions and beliefs.
But regarding my particular items specifically the "need" of a linear PSU for the amp in question, there is no scientifc testing or neither double blind testing.
Also how the user reviews are written also tells me something. That's exactly why i originally wanted to get the THXAAA 789 because it performed well here and the feedback from owners is also really good. But for instance, that AMP is a really great value for it's money, that's why it's so popular, but the natural question that comes to mind then how does an amp sound that provides more value in terms of performance?
, some say they don't because not everything is measurable. For instance, even capacitors impact the sound, is that measurable? Swapping OP amps also changes/improves the sound, is that measurable?
That again for me means two conflicting opinions.