Well you can't use the RCA's... but you can use the high level input. The high level input should utilize a type of wiring harness, with a ground, and two signals. The amp should have come with instructions. Tap that wiring harness into the speaker wires closest to where you are putting the tube, i.e. your rear speaker wires leading up to your rear speakers. Then, you can either run a wire from your power antenna to the amp for the on/off signal, or rig something else of the like. You could even just wire it to a switch if you wanted to.

BTW-markedly?