Well, first the Def Tech subs don't really play as low or even close to the rated specs. I have the SC8000 corner loaded in a 1650 cubic foot sealed room and for the most part is plenty for my needs.
As for the SC4000 and ML 700, if pricing were the same I would go for the SC just for the remote which is very handy. I would thing output would be similar although the ML might actually dig a little deeper.
My Def Tech is nice and tight for music at least IMO.
Klipsch RF-62II, RC-500, RS-400, SVS PC12+,
Def Tech SC8000
Harman Kardon AVR 1600
PS3, Apple TV, Sharp 70" Qattron