I said blind testing, not sighted testing. It is well documented that sighted testing is essentially useless in determining subtle differences.

When I was a test engineer at Altec Lansing, we performed literally hundereds of blind tests. During the design phase of one line of amplifiers, two amps were designed to be as identical as possible except that one was fully complementary (balanced) and one was conventional. The conventional amplifier sounded much better, and more like a tube reference amp than the balanced design. The balanced design was abandoned in favor of the conventional one.