I don't have an answer for you but I agree with johnson's recommendation....600 watts per sub will be more than enough to get them wanging pretty good.
I have an Arsenal 12 in a sealed 1.2 cube enclosure and getting 600 watts rms from a PG Octane 8.0:1 amp. It's by far the best sub that I've ever owned(Chad nailed his target of developing an outstanding SQL sub, IMO) so two of them should be loud as hell while still retaining excellent SQ.