Low watt system for rock,electronica?

I bet the system described above sounded pretty good!
Rethm is extremaly fast and dynamic.

I think in order to play convincing electronica/ pop/ rock, you need both a good dynamic and flow and preferably with enough headroom to be able to go loud without a strain.

Personally, I prefer SET or even pushpull amps playing electronica than most solid state based systems.

Ray, as Audiokin, above implies, the system you described and liked answers your own question -- doesn't it :)!
I.e.:
Single driver main speaker, no crossover if possible / subwoofer for say 200Hz, down. This driver (a Lowther in Rethm's case) has a very strong magnetic field and can/should be able to reproduce dynamics and details in an excellent way. Simplifying a bit, having a very strong magnet and low mms, the driver is usually very efficient; a front-loaded horn also increasing its efficiency even further. Efficiency + dynamics means, that speaker system driven by a lower watt, low distortion amp can produce realistic sound levels AND good/excellent sound and detail. An SET is low distortion within its optimum operating range (remember, we've left the low frequencies out of the set's range).

Indeed some such systems I've heard are more than good, they're spectacular!

depends on the speaker's sensitvity, doesn't it?

Coincident, Audio Note, Avante-Gard, Von Schweikert dB 100's.
I have heard the first 2 and they do a good job on a couple of watts. Coincident / Atma-sphere (20 watt??) was awesome combo but it WAS NOT cheap.

Cdc,
Avant-gard has powered woofers 150wpc so this one is out of list.
Vons like some current to give out bass.
Coincident arn't rock speakers at all.