Well, since you got the dual 4ohm version, you'll need to get an amp that's 1ohm stable, because you'll get a final impedance of either 4ohms or 1ohm, and running the amp at 1ohm, if it's stable will give you more power than at 4.
I'm glad to see someone use the word "stable" in this reference. There can be considerable difference in being 1 ohm "safe" and being 1 ohm "stable". Stable is the amp's ability to remain constant or consistent over a range of use. This ability has much to do with build quality AND matching components in the amp's construction. An amp can conceivably be "safe" to use into 1 ohm and not necessarily be "stable". Stability has a price though, but in car audio you usually get what you pay for.