As far as DBT, I've been a part of many DBT drug studies because pharmacists are the only ones to know which drug is which.
I have never been part of a professionally sponsored audio SBT or DBT.
When I had my collection of speakers, I did conduct informal speaker SBT (certainly not to pro standard by a long shot).
I have never done BT on solid amps. In my experience (Krell, Mark Levinson, Lexicon, Classe, Bryston, Anthem, ATI, Macintosh, NAD, Sunfire, Parasound, Rotel), when level matched close enough, the difference is just too insignificant. Too subtle. You want to hear subtleties, you can have them. But if the difference is too subtle and not significant, why argue over it?
But when someone says there is a night-and-day unequivocal astronomical difference between NAD vs Parasound or Outlaw amps even when level-matched using the same equipment and music source, I have my reservation.