I've been stuying the topic for some time now, as much as work permitted, and came to a few conclusions. Mostly read work from Linkwitz and JohnK. Above the schroder frequency, the best sound is achievable by either making the room very dead, absorptive, or by employing speakers designed for controlled directivity (whichever way, horns, dipoles, large baffles, should work). Below the Schroder frequency, best approach seems to be dual subs, with apparently dipole or cardioid dispersion. For smaller normal (not overly or at all acoustically treated) rooms, cardioid bass might be better as it would behave like omni below the first fundamental, benefiting from room gain. For larger rooms, dipole stereo bass when set up properly should in theory be best. For smaller rooms, it might also be befeficial to use tightly packed speakers like coaxials or similar due to better integration. Did I miss something? After building and living with lx521, I'm planning to design my own version of full range dipoles, but ones that are even slimmer. Actually, I'll try to make them simmilar to gainphile's s20Z, footprint - wise.