Speaker sensitivity vs SQ

Wait, did we just enter the "speakers should be made of wood, brass and silver because that's what musical instruments are made of" world?

The principles of measuring a good sounding room have been well documented for decades.  The measure of only using things that appear in nature is silly.  Does your drywall reflect any sort of natural space?? No, it does not.

If the room acoustics aren't removing the excess noise, then your brain is, and that's tiring.

The thermal distortions in speakers and transistors have inertia and therefore are a heavier burden on our brain than conventional non-linear distortions.
In addition, changing the impedance of the speakers changes the frequency of the speaker filters, which leads to different sound at different volumes and issues with frequency and phase response. Electrical Q is changed that changes bass response.
The proper built SET don’t have issues with bass (with high efficient speakers). The problem is too many bad SET designs.

Sorry Duke, my bad. My point is that dynamics are a matter of volume. A speaker that can hit 110dB without compression is going to be more dynamic than a speaker that can only get to 100 dB even if it is less. efficient. Just a matter of power. Horns are very dynamic because they go very loud. They do it with less power because they tend to be very efficient. As far as sound quality goes, it's a toss up.
Another issue is trying to run 15" woofers up to 700Hz then crossing to a horn. Two very dissimilar drivers crossed right in the meat of the midrange. You really have to push that crossover lower and in order to do it you are stuck adding a tweeter. I'm  all in for limiting crossovers but horns have their limitations in this regard. This is what makes ESLs so special. You can easily get them to go from 100 Hz to 25kHz. Obviously you can make them go lower but IMHO you are much better off going to subwoofer especially if you can use a digital crossover. 
Audio2design, I know for  fact  you do not have to have active loud speakers to take advantage of digital signal processing. Perhaps it will be the way the market goes but I am not so sure and I am an unabashed huge fan of digital signal processing just check out my system page.
Alexberger, in order to have inertia you have to have mass. Thermal distortion (whatever that is ) certainly has no mass. You are more than welcome to your SET amps. They are most definitely not my cup of tea.
I have heard several speakers in an anechoic chamber and they sounded just fine. You can test your own by just moving them outside. Tuning a speaker in an anechoic environment is a fine way of achieving a flat curve or rather the curve you want. In order to tell what your speaker is really doing it is the only way. What happens in a room depends on the speaker's dispersion characteristics and the room itself. A speaker that is more directional will sound very similar in room as in an anechoic chamber. Controlled dispersion is the best room treatment you can get followed by digital room control (speaker control) and a few foam tiles. 

overdamped Eric...