Best Tube Amp For Sonus Faber? Or Pass XA-100.5? $6-7,500 Budget, Purchasing Used.

At the point of making a final decision now. In rereading this discussion, I was struck by jmcgrogan's early comment that 
 
"I tend to agree with George, I'm not sure that a tube amp would work well with the Sonus Faber Olympica III's, they are not an easy load.

Any VAC amp that can put out 100 wpc and use KT-150 tubes though MAY be able to do it.

I was actually using a VAC 160iSE integrated amp before the XA-100.5 mono-blocks, and my speakers have similar specs (90 dB, 5 ohm versus your 90 dB, 4 ohm).

Switching to the XA-100.5 amps, the sound-stage opened up immensely. Not really surprising going from a tube stereo amp to SS mono-block amps.
Mating the Pass amps with an ARC Ref 5 preamp, the resolution of the highs and lows also became more extended and defined.

The only place I would give the edge to the VAC was in the midrange.
Though the Pass are quite warm and musical, the VAC had that touch of *magic* in the midrange, that fuzz on the peach quality, that only a tube amp can do."

I would suspect the sound from the upper level PHI power amp would improve over the VAC integrated that you had, possibly not in a huge leap, though. And it sounds like your satisfaction was clearly greater with the the Pass 100.5's, excepting the extra touch of tube magic in the midrange.

Going into this, I had really been leaning toward the 100.5's, and as I noted before, had been on a waiting list for a pair at Reno HiFi for the past year. I love the look of those amps, and would have bought an available pair (had one shown up) except for the fact that someone whose knowledge I truly trust, and who has owned and enjoyed about half the Pass line of power amps said they were his least favorite because the bass was puffy and inadequate. 

I should perhaps have mentioned that a big part of originally wanting thr 100.5's had to do with how impressed I was after hearing the 60.5's (not enough power for my speakers) and recalling John Atkinson's review a couple years back calling those the best amplifiers he had ever heard. As a followup, I was told that the 100.5's were essentially the 60.5's upscaled, which doesn't seem to be the case?

The new IQ continuous auto bias in the latest VAC amps are a night and day difference from their prior 160, 200, 300 phi models.  Far more smoother and transparent, tighter bass, etc and more stable power output makes it a lot easier to handle all speakers.  I owned the VAC and as well as the SF Olympicas and the Elipsa and handled them fine.  the VACs are paired with Magicos, Focals, Vandersteens, Sonus Fabers, Harbeths, and know they can drive them well, even with the stock KT88s.   But if you're in love with the PASS LABS, then you it seems like you found what the sound you're after.

I have an Audio Research VM-220 that I just got checked out and put new 6550 tubes (from AR!) that I will be listing shortly.  These monos powered my Sonus wonderfully, but with 12 tubes in each, the room can get warm.  Great sound though. - PM me if interested.

I should perhaps have mentioned that a big part of originally wanting the 100.5's had to do with how impressed I was after hearing the 60.5's (not enough power for my speakers) and recalling John Atkinson's review a couple years back calling those the best amplifiers he had ever heard. As a followup, I was told that the 100.5's were essentially the 60.5's up-scaled, which doesn't seem to be the case?

All Pass amps seem to have a slightly different sonic signature. From what I understand, the XA160.5 is the next logical step up in power and flavor from the XA60.5. I've had many Pass amps, and while the highs and mids were wonderful on XA100.5, the bass seemed bloated to me. Some say it the most tube-like of the amps but, to me, not in a good way. The XA60.5 were amazing sounding amps (I love the XA60.8 and X350.8 as well). I love Pass, if you can handle the heat. My favorite right now is the X350.8. Several friends have them and I always look forward to going to see them and listen to their systems.