Rocky,
I have an SVS 20-39CS+ currently. I actually just dropped from 2 of them down to 1. After experimenting with some room treatment I have realized my room is small enough for 1 sub and I did not need 2 subs, but instead needed to soak up some of the reflections with all the wood paneling I have in the room.
The Def Tech PF12 got moved upstairs in the living room setup when I upgraded to the SVS subs a few years ago and gets used about once or twice a month. My wife does not want it in the living room anymore so in the interest of having my say only in my dedicated HT room downstairs, I am going to let her win this battle. It is a great sub it just doesn't go as low as the SVS I have.