I have some bad news for you. I recently went through the same thing you're going through with my 2001 GT Convertible. It turns out the Mach 460 system changed from 2000 to 2001 and it isn't easy to simply add an Empeg to the rest of the system. In 2000 and earlier Mustangs, all amps and crossovers were external to the head unit. Installing the Empeg was a simple matter of wiring up an adapter harness from one of the 3rd party harnesses available. The levels out of the Empeg were just a hair less than the amps wanted and everything worked fine. Unfortunately in the 2001 (and later I assume) Mustangs, they changed things to a single head unit which appears to contain the crossovers and amp for the tweeters. I theory I suppose you could add an amp and crossover to use the factory speakers. In my case, I decided I was better off replacing everything and added my own amp and new front speakers. I also decided to forgo the rear speakers in the hopes of a better front soundstage. Let me know if you have any questions if you decide to go that route. - Eric