type-e's sound like ***. My pioneers were much better. With the price of the mb quarts i'm going to a few just for fun. I've heard them in a ported enclosure before and they sounded good. I'll be going sealed with 3 of them though.
keep the subs you have now they are 400wrms you are giving them 500 combined. this amp will give them a bit over 800 which is much closer to their actual rating
You might be able to pull a lot of things off if you find a great deal
On your budget you're going to be hard pressed to find anything over 500-600 rms total. You might have to go with 10s or 8s. 2 RE RE 8s/10s/12s on 500 rms would be under budget and decent. Not great, but $231 for a sub/amp combo is hard to do.