If it was up to me I would seriously consider the M&K X15 Plus, or even better, the Perlisten D215s. These are the only THX Dominus certified subs out there. Dominus means 95 DB continuous and 115 DB peaks, in a 6.500 cubic foot room with a 20 feet listening distance. The M&K X15 Plus is $5,999 each, while the Perlisten is $8,999 each.
Best