"I know that the stiffer and less resonant the cabinet is the better it sounds" You do? The people at Living Voice don't, and they know a thing or two about making speakers:
http://www.6moons.com/audioreviews/livingvoice5/1.html
"The right type of chipboard created a naturally vibrant, energetic, powerful and radiant sound. Thicker panels diminished those qualities. Hence we use 18mm thickness, not the 22 or 24 which any marketing man would prefer. "
The cabinet stops acoustic waves from traveling around the speaker cone, hitting it on the rear and thereby canceling the signal. There are speakers with no cabinet but they still have a bit of a baffle and use huge cones to overcome at least part of this cancellation effect.
http://www.6moons.com/audioreviews/jamo/909.html
Others, like Nola, just use a cabinet for the woofers but have the midrange and tweeters on an open baffle because the acoustic wave from them is more directional and does not affect the rear of the driver in the same way as the acoustic wave from a woofer. A speaker hung in mid air with no cabinet is not going to produce any useful bass.