Low power tube amp for Sonus Faber?

The Evolution 845 is the amplifier I was hoping to suggest and it looks like it is already on your radar.  The Compact 845 is an excellent amplifier, but might not be right for every situation.  In this case, I do think the Evolution 845 would be the top contender.  The price is much higher, but so is the performance.

Like Charles has hinted at, the transformers are massively beefed up in the Evolution 845, bringing the weight up from 75 lbs to 117 lbs.  I have had a few speakers in house where the Compact 845 was just not the right bill and for every one of those speakers, the Evolution 845 lit them up.  

The Evolution 845 is a statement piece that I have yet to find a poor match with.  I'm not saying they aren't out there, but they haven't presented themselves yet.  Even on Martin Logans, the amp has performed magnificently.

Audiothesis,
Thanks for the additional amplifier information, it confirms what I suspected. All design and built parameters of a power amplifier have to be considered. 50 watt amps of the caliber of this Mastersound Evolution can manage speaker loads that some higher wattage amplifiers can druggie with. Just saying that ’X’ amount of power is sufficient doesn’t account for the entire picture/scenario.

I recall a situation described by an Audiogon member Raquel ( former TAS reviewer I believe ) several years ago. At a demonstration a 750 watt VTL was having a very tough time driving a pair of speakers. They replaced the big VTL with a VAC Renaissance 70/70 (65 watt) amplifier that easily drove the same speakers. Obviously this suggests very different design aspects of the two tube amplifiers.

The VTL wasn’t a bad amplifier by any stretch, just a poor match with these speakers despite the very high rated power. Power supply and transformer quality are crucial considerations in the big picture with regard to tube amplifiers.
Charles

Just found this review by Jeff from Tone Audio: 

"With a wide range of amplifiers at my disposal—solid-state, tube and class D amps, ranging from a pair of 20-watt 845 SET monoblocks all the way up to the mighty Pass Labs’ XA200.5 monoblocks—all were able to drive the Elipsa SEs without difficulty. Granted, each amplifier imposed its own sonic personality on the presentation, which complements the high resolution that these speakers offer. But still, every variation on the theme remained thoroughly enjoyable.

Thanks to a sensitivity of 91 db per watt, the Elipsa SE is comfortable with the 35 watts per channel that the average EL34-based tube amplifier can provide, but because the speakers have a maximum power handling of 300 watts, they will absolutely crank if you have enough high-quality power on tap"

I know that you have to double the power to get 3db increase in sound, and evolution 845 55W isn't quite double that of compact 30W power. But something tells me it isn't all that simple, and more power will still sound better overall, even if I don't push the amp to its maximum.