first off, make sure your car can handle the current load of the amps (most likely over 200amps draw) chances are, that 1500 alone is taxing your electrical to death. even with a real good battery and "big3" along with appropriate sized cable, your alternator(s) need to keep up, or it will just drain the whole system down. mine and my buddy's tahoes came with 160a alts stock, and i can maintain 120amp draw, but he can't power a pair of 1200's, which is less than you are talking about doing. power supply aside, yoiu need to run distribution/fuse blocks back by the amps, and you should be able to run one amp off the other, as far as the rca's are concerned. just hook one amp to where the other amp says "output" on the rca connections. you can also just run another remote wire from one amp to the other. rule of thumb is that you can run 3 devices off the one wire. as far as adding smaller subs to work in conjunction with the larger subs, it really is not going to work, or at least work well. there will be cancellation form the 2 different tuning, and they will cause abuse to the other set when they are out of their frequency range. for example, the 10's will get pounded on in the lows, and the output of the 10's can get counter-acted (canceled out) by the 12's outside of their tuning, where they are already experiencing cancellation, or they will absorb some sound if the amp is tuned to not even put out power at those frequencies. only time i can see this kind of set-up working, is when you have 8's or 10's in the doors, or sealed up in the rear deck, and the lows playing in the trunk. there you have 2 different effects going on in 2 different spaces, both effecting the front cabbin. just what is your current setup/options?