Factory stereo system:
The Mustang's standard stereo was an 80-watt, 4-speaker system featuring an AM/FM/CD player that gained the ability to play MP3 files in 2002. The next step up was the Mach 460 system, which offered a 6-disc AM/FM/CD receiver with, coincidentally enough, 460 watts of stereo output pumping through a total of eight speakers.
Mind you, that's the peak power rating, not the more meaningful RMS rating, but that's still a ton of power for a "factory" system. The Mach 460's added power came from a pair of amps mounted between the rear seats and the trunk. The amps took care of the lower door speakers and rear deck speakers, while the front and rear tweeters ran off the stock receiver.
With ten speakers and six amps, the Mach 1000 system, which debuted in '02, was to factory audio what the old Boss 429 Mustang was to factory horsepower – wonderful, glorious, American excess. The trunk was a veritable stereo shop on wheels, two enclosed subs on the sides and the four amps that powered them lined up on a rack in the center.
Needless to say, the Mach 1000 produced a prodigious amount of power. An aftermarket system will sound better, especially after all these years, but Ford deserves massive credit for shoehorning a real hot rod of a system into this car.