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.
The XA-100.5's do get quite warm after a couple of hours, but I wouldn't say they turned the listening room into a sauna. They aren't close to the hottest amp I've ever owned (BAT VK-75SE). However, they are quite a bit warmer than the Jeff Rowland Model 6 mono's.
Another amp to consider, since you want tubes, but don't really have tube friendly speakers, is an Aesthetix Atlas.
A hybrid amp with 400 wpc into your 4 ohm load, but with a pair of 6SN7 tubes in the driver stage.
Just a thought.