I used to own the original Micro ZOTL and used it on high efficiency speakers and it did quite well, were talking 98 - 104 dB. Again, I think a lot has to do with how large your room is and how loud you listen.
The ESL panels I am using now have adjustable sensitivity, from 70 - 80 dB. The impedance is pretty acceptable from 100 Hz to about 10K Hz whereupon it begins to drop down to 2 ohm pretty quickly (note the speakers do not go below 100 Hz and I bi-amp them).
Understanding the designers goal was to make a panel with a very small footprint that can provide extensive detail at low volume, he had to make significant comprises. So he said the heck with the rest of it and made a set of panels that are better than my ESL-57s, but not as flexible with amplification. While the recommendation was to use a 100 watt amp (ss or tube) I was able to use a tube amp that is 35 watts per channel to drive them cleanly getting SPL levels up to 90 dB, which is a good 10 dB more than my preferred listening level. The level of detail and clarity in the music is fantastic.
In addition to room size and listening levels, if an amps damping factor is synergistic with a speaker, a lot can be done with a little power. There is too much emphasis placed on headroom in 2-channel. although in home theater I think it's important. Less is more in many cases. Mind you I'm talking about the ability of an amp to drive a speaker cleanly to reasonable listening levels. Just because it can be done doesn't mean the listener will like how it sounds.
The ESL panels I am using now have adjustable sensitivity, from 70 - 80 dB. The impedance is pretty acceptable from 100 Hz to about 10K Hz whereupon it begins to drop down to 2 ohm pretty quickly (note the speakers do not go below 100 Hz and I bi-amp them).
Understanding the designers goal was to make a panel with a very small footprint that can provide extensive detail at low volume, he had to make significant comprises. So he said the heck with the rest of it and made a set of panels that are better than my ESL-57s, but not as flexible with amplification. While the recommendation was to use a 100 watt amp (ss or tube) I was able to use a tube amp that is 35 watts per channel to drive them cleanly getting SPL levels up to 90 dB, which is a good 10 dB more than my preferred listening level. The level of detail and clarity in the music is fantastic.
In addition to room size and listening levels, if an amps damping factor is synergistic with a speaker, a lot can be done with a little power. There is too much emphasis placed on headroom in 2-channel. although in home theater I think it's important. Less is more in many cases. Mind you I'm talking about the ability of an amp to drive a speaker cleanly to reasonable listening levels. Just because it can be done doesn't mean the listener will like how it sounds.