BMO, I'm all for equal time, and a competitive marketplace -- sorry if my last post seemed a little 'SVS centric' ---
But in 6500 cubic feet, neither AV123 or Hsu has currently available product IMO.
Come January, hopefully, the Hsu VTF-3 HO will be out of preorder fulfillment.
A pair of Seaton modded UFW12's might work -- again, not yet available
MFW-15, BMF --- not yet available
Axiom -- I'l refer you to Ilkka's test:
http://www.hometheatershack.com/forums/subwoofer-tests/973-axiom-ep-600-a.html
Compare it with some of the others.
And Axiom does not include continuously variable phase controls on their subs.
If you are only using one sub, or co-located subs, you can use a continuously variable global phase control (if you have one in your prepro, SMS-1, etc) to blend with your mains, but if you are going to place the subs in separate locations you need a continuosly adjustable phase control on each sub.
BTW, SVS has a 45 day money back guarantee.