My buddy has a Mach 460 system in his 2000 GT, and none of his speakers work. He also has an aftermarket amp with two subs hooked up in the trunk that work just fine. His deck works fine and puts out signal (since the subs work), but none of his factory speakers work. Any ideas on this? How many amps are there that power the factory system? Which fuses are for these amps? (I'm not to stereo-oriented, so bear with me)