i currently own Pass Labs XA160.8 ( feeding it directly from Chord Dave DAC ) had Audio Research REF 6 as a home demo and i could not belie how much sound quality improved making listening experience more enjoyable. I always thought that having most direct connection in the signal path was the best but after trying AR Ref6 i now think differently.
if possible can you describe how it compares to Luxman 900u,, something i'm thinking on trying, I really really love my pass labs ( came from Parasound JC1s and for money i think they are best set of the monoblocks that you can get in 4K range used ....
Also interested in Diablo 300 ( assuming that is what you had ) I've only listened to it at the dealers listening room with Focal Sopra 2.
I have Sopra 2s as my main speakers