George,
You are correct that many amps, but I will add not just class D, will not keep doubling their maximum power output from 4 to 2 ohms. Once the max current capability is reached, say at 4 ohms, then at 2 ohms the max power is only 50% of that at 4 ohms. 50% lower than that, or 25% at 1 ohm. This is particularly important for electrostatics whose impedance could be 1 ohm at HF. With some music that has high power HF percussion in triangles, snare drum and cymbal crashes, that is a big problem.
An example is my Bryston 2.5B SST2 amp, which puts out 135 watts at 8 ohms, only 180 at 4 ohms. The Bryston tech estimated only 100 at 2 ohms, and probably only 50 at 1 ohm. The larger Bryston 4B SST2 puts out 300 at 8 ohms, 500 at 4 ohms, and the tech estimated 600-700 at 2 ohms. Definitely better, but unfortunately all this doesn't correlate with the sound. Despite Bryston's official line that all the amps in the series with different outputs sound the same, my listening at home with the 2.5B SST2 shows much better transients and clarity vs the 4B SST2. With the 2.5, inferior power specs but better sound within its power limitations.
