Klipsch has\/had THX Ultra2 speakers system - quite expensive, but from what I heard very competent.\nM&K also has THX speakers, for example - V12 sub is THX Select certified\nA sealed 12" sub with 300w rms amp and +\/- 2db 20-200\nLets say sounds somewhat similar to SVS SB2000? - It does to me, except it's double the price of SB2000 !!\nTHX Select isn't that tough to achieve. The sub still has to have a linear response, and low distortion. Once you get to THX Ultra is where things get really demanding. And I doubt you will ever see a sub achieve the THX Dominus certification. The subwoofer than can do that would have to be pretty spectacular.