sounds to me like you're better off letting a pro do it. Also i'm pretty sure this lc2i will not work since it only has 2 inputs, if i remember right on our cars you need 3 so you'd need something like this
http://www.jlaudio.com/cl-ssi-car-au...egration-98112
The biggest issue is that you have to find the wire harness for audio, identify speaker wires for each channel then cut wires and feed them to summing interface