Hello I have a 2005 Mustang. I recently installed a set of alpine SPX components in the doors and i replace the stock 8's with a set of CDT EF8s 4ohm SVC

I think the alpines can handle 60watts at 4Ohms and the CDTs can handle 200 Watts

I was looking at a Kicker ZX550.3 to run every thing.

RMS Power in Watts

@14.4V, 4Ω Stereo ≤1% THD+N 70 x 2

@14.4V, 2Ω Stereo, ≤1% THD+N 85 x 2

@14.4V, 4Ω Mono, ≤1% THD+N N/A

RMS Power in Watts, Subwoofer channel driven

@14.4V, 4Ω Mono ≤1.5% THD+N 210 x 1

@14.4V, 2Ω Mono, ≤1.5% THD+N 420 x 1

Can i run the alpines on the 4ohm channels (70x2) and the CDT's in parallel give me 2Ohms and put on the 420x1 sub channel.

I guess is what i am asking if the one set of channels are wired 4ohm dose that mean the sub channel needs to also be wired in 4ohm?

You do not need to run them all the same. It sounds like the 3rd channel is its own seperate circuitry. The way your asking about setting it up sounds fine.