It depends... what Ohm does the amp put max power at? If it's 1 ohm then you need 2 ohm DVC's if it's 2 ohms then you need 4 ohm DVC's
My buddy has 2 15" L7's (4 ohm DVC's) and bridged them into 1 ohm VERY VERY LOUD!! can't see to drive because your eyeballs shake!!
you will have to bridge, so if using 2 , 4 ohm subs wired in parallel this will create 2 ohms. so iff you where doing a pair of 2 ohm that bridges to 1 ohm, or 3 6 ohm = 2 ohm etc. so at 2 ohm you are getting your max output.