Agreed, proper abx testing is difficult to set up and needs help which is not always forthcoming. I did one recently to compare Qobuz with Spotify. Kept everything identical except the streaming service and had my kid switch for me. I picked Qobuz for 8 of the 10 track segments where Qobuz offered a hires stream. That kinda settled it for me, although some folks claim that Qobuz uses algorithmic equalization to make stuff sound better.
If you could pull it off and do it double blinded, and you still manage to score better than 5/10 consistently then you have very discerning capability, even then, you can't be sure you heard the difference unless you score much higher than that, it would simply mean the difference is so small that it may not be worth the extra effort and/or cost. I have tried it on the buckeye Hypex amp, a VTV Purifi amp, Bryston 4B SST, Parasound Halo A21, and a few other amps, never could hear a difference and my tests were not even truly DB, but just volume matched single blind though I did not try to know which devices I was listening to. FR measurements also showed they should sound the sound, based on FR and THD.
I would still buy a McIntosh amp but it will be just for the build quality and look, and that I always wanted one when I was a teenager many years ago, and it is very affordable, comparing them to other jewelry like amps such as D"agostino's. Other more expensive amps such as Boulder's look almost ugly to me lol... I wouldn't buy used though, but a dealer's demo may be okay for me if there are in brand new like condition.
