Best Paradigm or other Sub to go with my setup?


What I currently have:

Fronts- 7se MkIII
Center- CC-370 v.2

I don't have a lot of money, so I can't buy everything all at once, and ok with buying good used equipment. My hope is to eventually get a 7.1 system with maybe a Denon or Yamaha reciever using ADP surrounds. Can I use 2 sets of ADP-170's for both the side and rear surrrounds?

I've looked on Ebay and Audiogon. I can't see myself spending more than maybe $750 for a sub. What Paradigm subs would go well with what I'm planning? Or should I consider other brands? I've seen SVS mentioned on another forum as a brand to consider.
pffreese
Save some money and stick with 5.1. There is so little 7.1 material (even with bluray). I have a 7.1 HT set up and almost always (95%) use the 5.1 codec unless there is a 7.1 soundtrack (RARELY!).
Locally on Craigslist there's a JBL Northridge E150P for $200 and a Theater Solutions I believe RT350 for $100. Any opinions on these?
the jbl northridge is entry level stuff which will not be up the quality of the subs above mentioned. you can get much better for less. theater research sounds like a "white van" product and, if such, is worthless.