Let me break it down for you right quick!
Nexus makes powerfull amps, im not sure if you can find them but they put out alot of power the amp you want to look into would be the nexus lion! I hope you have some money, because you will need a bigger alternator for all those watts! I wouldn't do it but thats you!
I would like to suggest something for you, you may not like it but here it goes!
<--- go here look at there subs if you really want to be loud get either the 9012 or the 9512, or if they are too expensive for you grab a 3512 which i have and love, i used to have audiobahn then i went to digital designs!
Digital Designs breaks all kinds of records, alot of the top competitors use them, they are handbuilt in the usa, you can only order from them factory direct, since they don't sell to other car audio shops!
To me they are one of the best companys out there since they will rebuild you a sub, say you have your 9012 for like a year now maybe more, and you decide its not like it was when it was new, send it back to digital designs and they will gut the sub and put all new parts back in the sub, for half the price you payed for it!
What other company will do that for you???
Another good thing about there subs is you wont need 4000 watts either!