GM Monsoon Amp Questions

Since I am going to have to save money to get an aftermarket head unit, i will go ahead and use the factory HU for now. I can tap into the amps wires to feed my RF 3Sixty.3 but i don't know the smartest way to do this. The 2008 G6 Monsoon amp is located conveniently in the right rear corner of the trunk. Is anyone familiar with this amp? Or the proper way to tap into it for a signal to feed the 3Sixty to send to my amps? This will at least let me start this damn build.