I am sure this has been asked before, but I am not finding the answers I am looking for.

I have a 01 with the Mach 460 I am currently running two 10" subs with an external amp everything else is stock. I am going to change the head unit, I have the Metra 70-5519 harness, my questions are:

1. Which channel do I use in the back of the head unit for the 2 RCA jacks off of the Metra 70-5519 harness? Do those RCA jacks just run the two amps in the rears? I want to use the Sub channel on my head unit for my 10" subs not for the factory subs.

2. Does the Mach 460 have 2 amps or 3? I can see the 2 amps in the rear but I don't see one under the fatory radio.

3. I am assuming I need the +5V Fixed-Voltage Regulator from radio shack, I just want to make sure that is not built into the Metra wiring harness.

4. If I did want to use an external to amp to run the factory speakers or aftermarket speakers where can I tap into the factory speaker wires?