The "measurers" claim that if you can't put repeatable measurements on something, then it doesn't exist. This is stupidity at its most intransigent. \n\nWho are they? Was that kind of claim taken out of context, did such "measurers" qualify their statements with specifics? If they did, then I wouldn't know if I would agree with your "stupidity...." comment without seeing the whole thing.\n\nThe human brain is far more competent and subtle. An example I use is that you're walking down a crowded city street and hear music from a couple of blocks over. Despite the traffic noise and the multiple other noises distracting you, your brain knows instantly whether the music is live or recorded. No question, no hesitation, your brain knows. Measure THAT for me!\n\nI am not sure about the relevance in this. The difference between "live" and especially where no electronic gear is involved, and reproduced music at home is in fact huge, to the point even the half deaf would know the difference without measurements. Also true but to a lesser extent when comparing loudspeakers, say a pair of Revel Salon 2 to a pair of their entry level book shelf monitors under any conditions. In such comparison, no measurements would be needed to support the human brains. \n\nTo compare a XLS 2502 to an AVR such as a lowly AVR-X3500H with flimsy heat sinks in pure direct mode, when used well below their limits is a different story. In that case, I would go with measurements and not someone else subjective impressions. Measurements would then tell me at least the following:\n\nAt 5 W, the Denon receiver would have significantly lower distortions that the XLS 2502, about 0.0086% vs 0.0323%. At >150 W output (into 4 ohms two channel driven), the XLS 2502 would perform much better as the receiver would begin to clip.\n\nSo up to 100 W output level, we know the THD+N of the Crown amp would be almost 4 times higher (at lower levels) than that of the receiver. In terms of the threshold of audibility, it probably won't make a difference to most people, but iirc there were studies that indicated the Crown's THD+N level of 0.0323% may be discernible under some conditions, by some people.\n\nOn the subjective side, if someone tells me adding that Crown amp to a receiver such as the measured AVR-X3500H made a night and day difference even at low listening level, I would just say good for him\/her and I won't utter the word "Placebo effect".\n\nAgain, of course, ymmv.. I am simply trying to understand your points and my observations.