dual 2 or 4? and before this gets dragged out longer waiting for the answers i'll just ask: budget? do you do used/ebay? do you have the charging system upgrade for all this?
1) you need to post the specs of the sub/s you have i.e. the rms (not peak), the vc config (dual 2, dual 4, single 4, etc., brand is good.
2)budget. please post this before everyone starts suggesting amps that are say $500+ and 5 hours later you say it's only $150.
3)you buying brand new from dealer or online, used, ebay?
4)upgraded charging as in high output alternator, battery/ies, do the bug three. to run that amount of power you have to do it. might make you change your system plans.