Michael, of course lower noise and distortion levels are measurable and are made part of a unit's specs. The point is, however, that once these levels are inaudible to humans, reducing them still further(either in a different receiver or a separate amplifier), while showing good engineering, results in no audible benefit(note of course that Alan doesn't say that it does, and his past posts show that he certainly isn't into amplifier "sound").
Only carefully controlled blind listening tests can accurately examine these factors. The classic amplifier listening tests from
Stereo Review , which enraged some audiophiles(but opened the eyes and ears of others who were able to get their heads up out of the sand)illustrate the unreliability of open listening. Differences which were lavishly described before the blind tests began disappeared once the name plates and price tags also disappeared. Among the notable results was that the $12,000 pair of tube amplifiers(correctly designed without a flawed "tube sound")were indistinguishable from the $220 Pioneer receiver. So, we can't follow the old "Just trust your ears" mantra unless we make sure that we aren't allowing other influences to mislead us.
