I don't mean to be offensive, but stop making this so hard. Take the EASY way out and put this behind you.

Take that factory amp and THROW IT IN THE TRASH. Take your factory head unit and THROW IT IN THE TRASH.
Buy a nice JVC or Kenwood head unit (you can get nice stuff for under $100). Then buy a four channel amp, I recommend Kenwood.

Now, install the head and simply run 8 wires (two per channel) down to the amp area. Install the amp and wire it up.
Cut the connectors off the harness going to the speakers, and wire them up to the amp output. DONE.

Just don't push the volume too high, these newer amps are capable of overdriving the speakers in the car.

Point is, you will have AWESOME sound that the factory crap cannot provide. And you need not screw around looking for connectors, splicing wires, etc.