Bryston 4B3 vs Mac MC462 vs Pass Labs X250.8, OR... GRYPHON Diablo 300?

Hi,
Over the next few weeks I am organizing in-home demo of  three pre/power amps for my B&W 803D2's, and will purchase whichever sounds best.  I will be testing the following gear, which is based on what's available where live:
-Bryston B173 / 4B3-McIntosh C47 / MC462
-Pass Labs X250.8, if I can get my hands on one (will probably use the C47 pre-amp to test with this)
The Gryphon Diablo 300 is also a candidate.  I've seen some strong comments from others that Gryphon is in another league compared to the others.
My question is, barring what sounds best to me during my auditioning, in general to most people would the Diablo 300 really beat the others in my list?  And, are there any material disadvantages to sound quality considering the Diablo is an integrated vs the other choices?  I don't really care about having separates, but sound is obviously important.
Secondly related to the Gryphon, there is only one Gryphon dealer that is even remotely close to me.  Should that dealer cut ties down the road, or go out of business, does anyone know how I might go about getting service for the Diablo should I require it at some point?  Is that a valid concern?  There are multiple Mac dealers near me so that would not be so much of a concern.

Thanks in advance for any feedback....