Lin,
It does seem to me there are two extremes for best/optimal performance in general:
1) solid state amp + low efficiency speakers
2) tube amp + high efficiency speakers
Then there are all the greyer areas that lie in between.
I think there is merit to Almargs observation that flat impedance curves may work similarly well with both tube and SS. No clear advantage either way in that case. Which speakers specifically have that though?
Raplph's comment regarding bad interaction between high efficiency speakers and negative feedback makes sense also, I think. If so, that might help explain why high efficiency speakers do not seem to work as well with SS.
WHat if high efficiency and flat impedance curve though, like, Al's Daedalus? I wonder how many prefer SS versus tubes in that case? Are the preferences skewed on way or the other? Certainly, high efficiency (combined with higher, flat impedance especially perhaps) makes a smaller tube amp possible, opening up more possibilities there.
ANy other designs like the Daedalus in regards to high efficiency and flat impedance curve? I would especially be interested in smaller, less expensive designs to start if out there. I would expect smaller designs that do not attempt to plumb the depths of teh low end to be less problematic to be designed this way in general, perhaps opening up more possibilities?