[sr20de4evr]

Well if you want to start fresh don't go out and get the same crap you have in there now. I don't mean to be rude (I know I'm coming off like an asshole, lol), but IMO if you're going to do a system then do it right.

I don't really know what you're looking for in a system (sound quality, SPL, etc), but if you plan on using 15's you aren't going to get anything that even sounds decent unless you cough up the $$$ for something good.

If it were me I would ditch the idea of multiple 15's. If you get any 15" worth its weight in dog shit then just one of them will have enough output to make your hair stand on end, but it will cost you. Personally I would ditch the box, sell off the subs, sell the amp, and start fresh. Build a box for dual 12" or a single 15". Research everywhere before you pick your sub and amp, there are plenty of places to hear opinions (soundillusions, caraudioforum, here). It all depends on your budget really, but anything made by Elemental Designs, Resonant Engineering, Adire Audio, Image Dynamics, Crystal, and a few others will suit you great.