^^^as above mate...^^^ but my personal preference is only to use the amps built in crossover when running the sub(s) from it, and then again i would use the subwoofer pre-out to feed into this amp. is the amp you have 80 watts RMS each side, or just 80 watts MAX each side?? if 80 RMS each side, it would be fine to run the rears or even the fronts instead, your own preference - but as a rule of thumb, I always get an amplifier that can power (RMS) slightly more than what my speakers (RMS) can handle, so that i am not running the amplifier to its limits at all times if i want to crank it, or