Yes indeed, FM Acoustic gear is hard to find. Out of all the system you listened, may i asked which system gave the deepest and widest sound stage , Spatial cue, 3D feeling in relative to room size.
Again, this is very relative to rest of the set up. Mike's system with dart 458s far more than any other, but there is much more than the amp happening there. Apogee grands with modded Stax and plinius, but that doesn't mean I would recommend those amps.
All the others do soundstage etc very well, in most demos it will be limited by speakers and the room. If you are hearing one amp do more than the light without a direct compare you are probably hearing the speaker and the room.
FM and Vitus seem to have the most flow and tone. Vitus is slightly slower than the others. CH, boulder, spectral, are extremely fast. Gryphon is also fast. Boulder and spectral are also very clean sounding. Boulder can also sound very bright and artificial when not correctly set up. I am not a fan of being forced into a system like spectral. They will all do big soundstage, sufficient resolution. Your speakers and room will be the limiting factor.
In a non-analog system I personally would not prefer a very clean sounding amp, as I would need tone and flow, which a lot of digital lacks. This is easier with vinyl. So for a digital system I would go Vitus or FM.
