Advice on Amp and Sub Combo (SSA + Kenwood?)

So originally I thought that maybe I had the wrong box for this sub (120.9) and I had experimented around with several different enclosures with no significant change. I tried the recommended ported enclosure (ideal volume is 1.5 if I remember right?) and even tried tuning the port to exact recommendations. I tried a single sealed because I prefer sealed enclosures anyway that follow the volume knob better through all frequencies. I have always seemed to experience non-linear volume (its always really quiet even when its high volume until approx . I'm going nuts. I thought for a while it might be the amp, or the signal wires to the amp or maybe the HU. I tried different sources to just the amp. I agree there should be no way some JL 12w3's should hit harder or sound better than these infinities but I have no explanation for what's happened. Just looking at the sensitivity and rms rating you would think these infinities would be clearly the louder and better choice. I didn't have another amp to try until recently. Now I acquire my buddies gear for the testing and presto. I switch sub's w/box and all the issues are gone. I'm running the same 1 ohm configuration on the same amp w/ the same gain setting even. Now I can hear subs at low level, the volume stays consistent throughout my hour drive to work, they hit everything including bass drums on up, and they thump hard when I turn them up. I will switch my old subs to his box just to make sure I'm not missing something but I'm pretty convinced the 120.9's were the issue. Either way I'm ready for something else. Will the 900wrms kenwood amp be enough to push a single icon ssa 12? Should I be trying for something more tame?