Amps for B&W 805 Diamond: Rogue Audio or Krell, Pass labs, ML, Accuphase

The Medusa is a great amp with outstanding detail and 3D imaging/soundstage but I wouldn’t recommend it for the 805s unless you’re willing to do some tube rolling so of the two I’d side with the Krell.  With Pass I’d go with their XA series as it’ll likely play nicer with the diamond tweeter.  The Plinius SA103 is also a great choice, and it has a hi/low bias switch so despite being fully Class A you can leave it powered on or use it for less critical listening purposes without the amp running so hot.  Last recommendation would be the Clayton Audio S100, and if I had the 805s that would be my first choice.  Hope this helps and best of luck. 

The Medusa, while being an excellent amp, definitely leans to the more detailed/revealing end of the sonic spectrum (at least with the stock tubes) and I’d be concerned that this combined with the 805’s likewise very detailed diamond tweeter might make the sound come off as a bit overly bright sounding and potentially fatiguing on extended listening. If you can share what sound characteristics are most important to you and what improvements you’re looking for it would be very helpful in making recommendations better suited to your specific tastes. BTW, what amp are you using now and what’s the rest of the equipment in your system (including interconnects, speaker cables, power cords/conditioning) and what are your listening room dimensions?  The more info you give here the better the recommendations here will be. 

My most important sound characteristics are deep, soft, neat bass. Also a thick, warm mid-low and sparkling treble.

The only thing the Medusa will do well for you is the sparkling treble as its mids are not thick/meaty (although not thin) and the bass is about as tight and quick as any amp I’ve had in my system and nowhere near soft sounding. 
 

I don’t know if you’d have access to this used and fully-upgraded McCormack amp wherever you’re located, but given what you’re looking for I’d be all over this incredible amp because I think it absolutely nails the sound profile you’re looking for and is being offered at a very fair price.   I have the same amp at SMcAudio getting very similar upgrades now and can’t wait to get it back because with Steve’s upgrades these amps are thought to be at a near SOTA level. 
https://www.usaudiomart.com/details/649875150-smc-audio-modified-mccormack-dna-5-ultra-mod-with-gravity-base/

Or there are the other amps I mentioned before that I think would also be excellent except maybe not as much sparkling treble.  Other amps you might look into are Belles and Parasound.  Hope this helps. 

Well, I’d rule out the Medusa for previously mentioned reasons, and I’d rule out McIntosh because the treble will likely be too reserved for your tastes.  I’m not familiar enough with Krell as they seem to have shifted back to their more classic sound, which is a good thing so worth exploring.  If looking at Pass I think the X150 would be the one to focus on as the XA series might be a little too soft in the treble for your tastes.  The one that intrigues me is the Plinius P10 that is considerably cheaper than the others but seems to exhibit sound characteristics that are close inline with what you’re looking for.  This review may be of interest to you…

https://www.whathifi.com/plinius/p10/review

Thats all I got for now, and I’d encourage you to read as many reviews as you can on these three amps to see if one seems better suited to what you’re looking for than the others. 

I completely defer to @audphile1 as nothing beats actual personal experience, and I stand corrected.