[ZPM]

My stock head unit was marked "Panasonic" and had terrible audio quality. In your case, with no Monsoon, just do a normal full-install. New head and a 5-channel amp. You can buy the stock sub enclosure used or new. Or custom build something if you want more than 8" diameter. The one tricky part is that the car's chimes are run into the stock head unit and out of your speakers. There is an aftermarket interface box that has it's own tiny speaker in it. The interface plugs into your car's stock harness and routes chime commands to it's little speaker. Gets your sound system out of the mix. You can search my old posts on this for the mfg and part number. May have been Schoche, I can't recall. Or, you can just eliminate the chimes from your car and lose the steering wheel controls.

Oh, the interface also provides a way to retain use of the steering wheel stereo controls.

 

[ZPM]

On the Monsoon stock sub driver, I found that it's polarity is backwards from the factory. Also, while I swapped it for a Pioneer, I'd stick with the stock one if I had it over. Barely any difference in sound. One thing that's useful is to make sure the enclosure is 100% airtight. I also used dense foam to create a good seal between the face of the driver (mounted in the enclosure) and the big plastic facia that goes behind the seats. Trying to make sure all the air pressure goes out of the grille rather than dissipating some behind the facia. All this helped a lot, and at 8" you need all the help you an get!