Yah the MP3 system (with the h/u 02MGGT posted) is the 4 speaker sound system. I believe it was available on the standard and deluxe v6 models starting in 02 went till 04. (until the shaker system began in the new 05 platform)
It's not a bad system by any means and actually is way easier to splice aftermarket amps and subs into since all the p.i.t.a. Mach 460/1000 wiring isn't everywhere.
Here's a site with some Mach systems info:
Mach 460 Information
12 Black GT500 SVT PP l VMP TVS l JLT123 l O/R X l 28x11.50Rx15 M/T Street R's l BMR Suspension l Recaros
03 Sonic Blue 3.8 / 17 Magnetic Fusion Sport 2.7 EB