Hooking up amplifier to car speakers.?

I am planing on hooking up an amp to my new JL speakers that take around 60 rms. I was curious about wiring the amplifier somewhat through my sub amplifier. I would run a separate power wire for the amp so it would get its own power, but i was wondering if i could put the RCA's in the output of my sub amp then run them into the input of my speaker amp. Would this only transmit bass frequency? because i have my deck set on subwoofer out which is what my sub amp is connected to. Also i wanted to do this same thing with the remote wire in order to avoid too much rewiring. I also have another set of outputs in my deck for R and L, but i herd you cant use two outs at the same time. is this true? sorry i know its long, but thanks for any help! Jesse