Yes Joe I would say if current limiting isn't a factor due to an impedence dip caused by the loudspeaker load (thiels and several panel designs), the power supply limitations would be the primary factor that would cause audible compression in a tube amp. Again matching the amp with the speaker is important. What else would cause a change in tonal character? I have heard this effect more with solid state than tubes. Im sure a ss amp on the order of a big Krell or Classe would not exhibit these characteristics with virtually any type of load; maybe the Apogee Scintillas? On the other hand I am aware of no tube amp that can drive a <1 ohm load. The issue isn't brute force so much as having the reserve to provide effortlessness during dynamic, demanding musical passages. It certainly doesn't hurt bass performance either. Even when a tube amp does clip it doesnt exhibit the type of compression that solid state does when it clips, which is most audible. I really am curious as to what tube amps you have listened to in your system? And if you still have the Silverline Sonata speakers with their 93db efficiency rating I can't imagine you hearing what you are describing concerning a tube amp, even an 20-30 watt SET if not the flea flicker 3-7 watters.