For a low budget of $150 or so the subwoofer offerings from parts-express should work well along with the used Paradigm model you are interested in. From the sounds of it your Kenwood sub is on life support with the "popping' and all. Its ready for the electronics bin.

http://www.parts-express.com/home.cfm

I’m armed and I’m drinking. You don’t want to listen to advice from me, amigo.

-Max Payne