And isn't this exactly the problem with all sighted evaluations? Any
visual difference, or any known difference between the units under
test, establishes a reason to believe [audible] differences would
exist.

This is what I found. Regardless of which connections we were using
(analof or optical), when we switched between players without the
listeners knowing which players we were using, they couldn't identify
ANY sonic differences. During a 2nd phase, we told the people which
player we were using, and they suddenly developed the ability to detect
differences because they knew when we were using a more expensive
player. During a third phase, we kept the listeners blind, and would
start with the least expensive player...we would then tell the people
that we were switching to a considerablly more expensive player, but
would in fact simply re-start the SAME unit, and they a few of them
claimed to hear differences! That was the breaker for me, it became
plain and obvious that people were "hearing" differences when they
knew, or at least *thought* that we had switched players.

And isn't this exactly the problem with all sighted evaluations? Any
visual difference, or any known difference between the units under
test, establishes a reason to believe [audible] differences would
exist.

And if you're the type of person who's mental status always makes it
seem as though the more expensive unit is really producing better
sound, then you'll always want the more expensive unit. I'm personally
willing to except the limitations of the human ear.