I've already upgraded mine to a Mach 460 system. Hardest part of the installation was finding all the different parts on eBay.
PARTS:
Mach radio/tape player
Optional: CD player
Mach front amp (mounts underneath the CD player, has 3 wiring plug connections instead of the normal 2)
2 Mach door tweeters
2 Mach door 6"x8" speakers (marked with "Z" on the magnet)
Mach rear speaker package tray, containing:
2 Mach rear 6"x8" speakers (different from door speakers by wiring connection)
2 Mach rear amps
Mach package tray wiring harness
Mach radio wiring harness (NOTE: there are separate harnesses for Mach systems with/without CD players)
Mach front wiring harness (runs from driver's kick panel to rear of door frame)
Mach rear wiring harness (runs from rear of door frame to package tray)
Optional: Mach rear package tray cover
Door trim panels with cutouts at the top to fit Mach tweeters
INSTALLATION:
Before beginning, I took out the driver's seat to give me more space to work in. You'll have to remove the driver's kick panel, the driver's sill plate, and the driver's side rear quarter trim panel and lift up the carpet to run the front-to-back wiring. The rear seat and passenger's side rear quarter trim panel need to be removed, IIRC, to get the normal package tray cover off, the speakers out, and the package tray installed. The door trim panels need to be removed to install the door speakers and tweeters.
Step 1: Remove the normal radio, radio wiring harness, and CD player if you have one. REMEMBER which plugs go where on the radio wiring harness. The Mach radio wiring harness is similar - it just has more plugs.
Step 2: Remove the normal front amp inside the dash.
Step 3: Install the Mach front amp in its place.
Step 4: Run the Mach radio wiring harness - it'll go from the center dash radio (and optionally the CD), plug into the Mach front amp, plug into the speaker connections, plug into a (power connection?), run under the instrument panel, screw into a ground on the fuse box under the instrument panel, and end at a spot underneath the driver's kick panel where the Mach front wiring harness will plug in.
Step 5: Remove the normal package tray cover, and the normal rear speakers. The wiring connections for the rear speakers will have plug-in spots on the Mach rear package tray.
Step 6: Install the Mach rear package tray. It comes UP into its rightful place from the trunk, so either have a friend hold it for you or prop it up with some textbooks/phone books (what I did) in the trunk while you screw the nuts on top to hold it from the rear seating space. Plug in the speaker connections to the package tray.
Step 7: Connect the Mach front and rear wiring harnesses and run it from the driver's kick panel to the package tray.
Step 8: Remove the normal door speakers. NOTE: The normal door speaker wiring connections are actually the connections that will go to the Mach TWEETERS. The wiring connections that will plug into the Mach door speakers are actually taped to main door wiring harness, unused until now. If you get this backwards, you will get the interesting effect (like I did) of pumping the bass signal through the tweeters.
Step 9: Install the door tweeters. Mine didn't come with screws, so I had to run to Lowe's and get some metric-sized small, short screws. I don't remember the actual size. Plug the normal door speaker wiring plugs into the tweeters.
Step 10: Untape the Mach door speaker wiring plugs, plug into the Mach door speakers, and install the Mach door speakers.
Now put all of your interior back together. You should be ready to go! It took me about 3 hours to take everything out and put it all back together. A faster worker with help could probably do it in about 1, 1.5 hours.
I don't think I missed anything. I upgraded it over a year ago, so my memory might have skipped something. If you have a question, feel free to ask.