Wiring sub and amp to AM headunit

Hey Everyone,



I had a quick question. I have a avic z2 headunit installed in my m3 with factory hk system (used metra harness for install). When I run my rca cables, can I wire straight to my aftermarket headunit? Or should I tap into the hk rear speaker wires from the factory amp?



And If I were to run rca cables to HU, would I run them in the middle or driver/passenger side ?



Thanks

Ravi