The distinction between pro monitors and consumer speakers is (a) color: black (b) high reliability: down time in a studio is expensive (c) quality control: they all must be as nearly as possible the same (d) output: recording engineers have a "deaf" wish. There is no difference in the sound - the performance target is the same (the "circle of confusion" for those of you who have read my stuff). Part of the cost of a pro product, and also of some high-end consumer speakers is the additional cost of end-of-line quality control and adjustment if necessary. Most products simply go into boxes and the consumer is the QA department.
With the M2 and the new smaller, more affordable 7 series (
http://www.jblpro.com/www/products/recording-broadcast/7-series#.VuL2mMf5jww
there is dedicated electronics with equalization based on anechoic measurements. The M2s are spectacular, large, heavy and expensive, but the essential design elements are in the 7 series. Although I "lust" after the M2s, they are not very practical for my HT. The 7 series sound just as good, and play plenty loud for a HT. No sculpted, hand polished rosewood though :-(
If you think that M2s are "efficient", consider that they are delivered with a 1 kW power amp for the woofer and the same for the horn + DSP. The horn driver is 20 ohms so it really needs the voltage swing, not the current. But in a typical HT much less power would do the job.
And, yes, the difference between them and cone/domes is that there is no discernible power compression at high sound levels. The high level distortions in horns of yesteryear (still on the market) have been substantially reduced by better throat designs. The new, better, compression drivers do not use metal, much less beryllium, diaphragms. And they go to 20 kHz. I love science!
I think I will wait for the powered versions, which I hope are in the works. Powered loudspeakers, or those with dedicated electronics are so sensible. The only reason for those monster monoblock arc-welder power amps is to drive high-end loudspeakers that are incompetently designed and have impedances that drop to 2 ohms or less. When the power amps are matched to the transducers, everything is smaller, cheaper and better, and electronic crossovers beat passive ones any day.
But then what would the audio journalists have to talk about? Wires? Spikes?