Remember, bass below 80hz is really non-directional. Why not try 1 sub and if you don't get enough "slam" then add a second. You may be amazed that in normal listening that you probably won't be able to tell if 1 sub is connected or two.
Two Subs Vs. One
Trying to augment the sound from a pair of Totem Hawks in a large room (rest of system is an Olive Musica server, Eastern Electric Minimax Pre, Classe CAP-150 Amp). I am doing some in-home auditions of affordable single subs (mostly REL) and really like what they do for the sound. So far, I am leaning toward two smaller subs, one behind each speaker (ie. REL Q108E's - I like the sound better in that position and it looks better - wife factor) versus one larger one in the corner (ie. REL R-205). Can't find two demo units of the same sub to audition the two-sub option and was wondering if anyone had experience with this comparison.