I connected my Amp to my Mach 460 system. It was kinda a pain in the *** . I tried to find a set of speaker outputs going into the factory amps, without success. So I found the speaker outputs coming straight out of the head unit. They come from the large square connector with 8 pins. It has a gray shielded wire bundle going into it.
I had to break the back of the connector to get into it and splice into the wires, but it still works perfect. From the head unit I ran a set of speaker wires to the trunk where I installed a line level converter to use RCA wires for the input into my amp.
You can check out the custom intall I did at
http://minot.com/~topel/stereo.htm
Good Luck