More domestic version of the gargantuesque SB-M1 which previsibly sold a little better... but not much at any rate: the SB-M3 is quite, quite rare.
The filter comprises low distortion choke coils, high-impedance wires, electrolytic and film caps and steep 18dB/octave slopes ; the cabinet is made of real wood (unlikethat of the the M5) and uses special internal joints to prevent resonances.

33cm Bass
1,5kg magnet with linear damper and 4-layer voice-coil

8cm Mid
GFRP voice-coil with copper-clad aluminium wire and 950g magnet

2,8cm High
laminated mica diaphragm ; 35kHz response with magnetic fluid ;
18,000Gauss with square magnet for closer mounting to mid driver for more coherent dispersion.

I've never heard any flat-driver loudspeaker (whether Technics', Sony's or Pioneer's) but do love the idea behind the engineering slant. I don't really understand why, really, none of these sold well, if at all for the ultra models. But then, the present NEXT flat panels don't seem to sell well either...