What would be the best amp for 4 12" single 4 ohm subs??

I have 4 600 watt MA Audio 12" single 4ohm subs. And I have them all hooked up to a 2500 SSL mono amp, wired at 1 ohm. now in my opinion, this should give me some MONSTER B right?!? no...before, in the same car I had 4 Powerb 600 watt 12's, with a crossfire CFA 1000D, it it hit way harder! is there any reason why with double the power, and brand new subs, it doesn't hit half as hard? does anyone have a reccomendation for a good amp? or should I just throw the crossfire back in? please give me some ideas before I go bonkers!! lol...thanks