i'm having trouble matching subs --> amps. in my bronco i can fit 6.5's up front and 6x8's (or 5.25's) in the back. i previously had infinity kappa's in front and polk ex's in the back, run off a PPC powerclass 450 amp. they're all in need of replacement. i want a single 4-channel amp to power the speakers, but i'm having trouble matching an amp's output to the speaker RMS powerhandling. i.e. some have 75W rms, some have 130W rms, and the amps have like 500w. how do i do this?