It depends on how you plan to wire them. I believe your choices are 1 ohm: 4 ohm: 16 ohm. Or you can get a 2-channel amp and bridge it into 4ohms or wire each sub to 2 ohms on its own channel. For the Impedance that would probably be best, otherwise your lookin at an expensive amp to put out 800 watts @ 4 ohms or you need to find an amp that puts out 800 watts @ 1 ohm.
The Hifonics 750D puts out 750 watts @ 1 ohm, thats close enough.