I'd love to know if they have.  IMO it's one of the main reasons why DBT testing for hifi isn't particularly meaningful.

OK, I will conceed that, in theory, a DBT is better than a sighted test of the same duration.  I do however think that proper, reliable evaluation of hifi can only be done over much longer periods of time, listening to a wide range of music where a DBT type arrangement is simply not possible.  Just as I wouldn't trust the results of a DBT that involved 16 tests of 1 minute each neither would I trust a 16 minute sighted A/B comparison unless the differences were so huge and obvious that there was absolutely no element of doubt (which doesn't happen often when comparing kit of a similar level).

As an example, when I recently compared using an Apogee Wyde-Eye digital coax cable against a (cheaper and supposedly inferior) Ixos optical cable between my transport and DAC the difference was as clear as day - there was no element of doubt.  The optical cable was clearly superior.  Note that in this case the result went against the psychology - the winner was the cheaper product that I already had a prejudice against.

OTOH, I recently had a friend's NAD S300 amplifier in my system on test and I couldn't swear that I would have been able to tell it apart from my Arcam FMJ A22 and I certainly couldn't pin down or describe what the differences were. 

Also, when I've compared analogue interconnect cables the differences I've heard have all been in the "I might be imagining it" category.  In general, I'll only change something if I can hear something that I'm definitely not imagining and if that's the case it doesn't need a DBT test to show it.

Michael.