@jo1mtb Hi and thats an excellent question. Its a difficult question because I heard them so far apart timewise. The 865 was a fine amp. At the time it seemed a little too chilly and clinical for me years ago. The Gryphon will find its audience and when I heard it it seemed a bit of a chameleon, maybe trying too hard to include some tube like cues. I wanted to want it but it just didn’t move me. The 866, for what it is, is simply amazing. As many of my posts indicate, I am biased toward tube amplification and am fortunate to have the room and the resources for multiple systems.
The Boulder checks all the boxes of the OP and the sound is sublime. If dead neutral is noon on the clock face and 11 oclock (warmer), the Boulder 865 would be at 2 oclock (cooler) to my ears, the 866 at 11. The Gryphon, I dont know maybe 10 oclock, maybe 11:30, its been too long. I believe though that if it had made a significant impression on me I would have bought it. I believe the DAC in the 866 is a real treat in this package. It is so well integrated, it performs far better than it has any right to and for many the 866 could be an end game piece. As Ive said before, and I realize I have a psychological problem in this regard, but somewhere in my house at all times there will always be a tube based system.
Another nice feature of the Boulder is the volume comes on ever so gently, maybe even too gradually for some. I would venture a guess to say that you could connect the 866 to horns and have tremendous range in the volume with an absolutely black background. How many of us have had systems where you maybe had usable volume range of only zero to 10 on your 100 step volume control and thats all? That isnt the boulder. On Sasha 2’s the listenable range for me is 40-65 and 70 is far too loud.
If you you like neutral with an ever so slight side dish of warmth, the Boulder 866 is the ticket. I find it humorous all the arguing over Luxman vs Accuphase vs Gryphon vs Pass vs whatever else. The Accuphase, Pass and Luxman don’t meet the OP’s spec qualifications and I find NONE of those in the same league as the Boulder. Some might prefer Gryphon, others the Boulder. Everyone should just go hear these amps for yourself, let your ears and your equipment align with your listening taste. The Boulder 866 isn’t quite as warm as the ARC reference separates it replaced but, given that I have tube based systems to listen to, I kindof feel like I have it all covered. I hope this helps.
Once again to the OP, listen to the choices out there and buy what you like, this is rarified air that you are flying in. Im not sure if things can get much better for an all in one streamer, dac, 200wpc at 8ohm that doubles into 4 ohms class ab amp than the Boulder. Listen, when you can afford to buy what you want, and at your budget you can, you should wait until you hear something that moves you.