"Apparently though, know one has been able to hear a difference in a DBT between audio components at all (amps, preamps). "I couldn't disagree more strongly. A low-powered SET sound very different from a high-powered SS amp Two gainclones using the same chip and topology can sound very different simply because they have different power supplies. There is no way that these two examples wouldn't be declared different in a DBT.
Where DBT can go seriously astray is if the participants are asked to choose which piece of equipment they prefer. The participants are very likely to make the "wrong" choice. DBT can never be used for preference.
Bob