Yes, it's been told many times, Peter, but you notice that the bottom line is carefully avoided by those who claim to hear these things, i.e. "Prove it". Maybe the classic Stereo Review blind test
should be noted again, especially the certainty of hearing differences which were described in open listening before the test compared with the random results shown during the testing. Again(and again, and again...)when the amplifiers have a flat frequency response and adequately low noise and distortion(all available at quite low cost)and the listening level is within 0.1dB for all, listeners can't distinguish between them, regardless of brand or cost. Where one or more of those factors are inadequate in some poorly-designed units(e.g. some tube amps)then a difference may be audible, but it would be as a result of measurable differences in those basic parameters, which instruments detect at levels far below human audibility.