think of it kind of like the ride in a car with crappy shocks vs a ride in a lexus
crappy shocks have you bouncing all over the place, but well tuned and well designed shocks keep you riding smoothly along when you get natural bumps in the road.
So they'll keep the room from shaking?
But seriously, how would vibration isolation HELP the performance of an amplifier, I can understand a CD player from read errors, but that's it?
Tube amps are affected by vibration, the effect is called "microphonics" because the tube responds to sounds as if it were a microphone.
Transformers and volume controls can exhibit this effect as well.
On the cheap, "gel" shoe insoles can be cut, doubled or tripled in thickness, and do a decent job of isolating.
If the sound level is high enough, the tube envelopes will be very hard to isolate.
If the amp must be subjected to high SPLs, it may be wiser to go SS.
( FYI, L-MOSFETS softclip much in the same way that a vacuum tube does...)
Tubes are cranky, sometimes expensive, and need TLC, but there is nothing that sounds exactly like them.