Gryphon Diablo 300 or Pass Labs Int-250 to Sonus faber Amati Tradition

I have the 300 and it is not "squeaky clean" nor "unforgiving" nor "brutally honest" - it is simply neutral compared to the 250. SF is a good speaker brand to match with Gryphon overall, especially if you want to retain the easy-going SF sonic character while injecting some dynamic jump/authority.

today i got mc452 and c2700. Is Pass Labs in the middle of Mcintosh and Gryphon?

Don’t rule out the Boulder 866. It is an excellent integrated amp. 

REGA OSIRIS can match up to these other contenders

there is no identifiable “ best” at this strata of equipment…only different bespoke sonic signatures for you to personally distill out to the one that  stirs your drink in terms of synergy with the rest of your system ( all of source, cables, and speakers)

It depends on what kind of sound you are looking for, I strongly recommend the Diablo, Amatis have a smooth personality and Pass 250 has it too, too much smothness in my opinion...