CVRs to TypeRs will give a small, noticible SQ difference, not necesarily good though, it depends on which one the listener prefers. If you have 1000wrms going to 2 15s in your trunk and have absolutely no more space to give up, I'm sorry to say you wont get any noticible SPL increase w/o spending some serious $$. You can get 2 more efficient subs and a higher wattage amp, but you'll be spending a good ammount of money for just a couple DBs. Ususaly someone like you should just go ported, but you dont have space. With unlimited funds I would say you should get a 200+amp alternator and a 2500+wrms amp and 2 CV strokers. Good luck with that though.