What would be the best upgrade for the Monsoon system?

If you want to 'upgrade' the existing system, the best and probably easiest think you could do would to be hook up an external amplifier using line-level converters and install a sub or 2 in the trunk. That will add some decent low-end and really fill out the sound. Otherwise you're pretty much looking at scrapping the factory system altogether.

If you want to 'upgrade' the existing system, the best and probably easiest think you could do would to be hook up an external amplifier using line-level converters and install a sub or 2 in the trunk. That will add some decent low-end and really fill out the sound. Otherwise you're pretty much looking at scrapping the factory system altogether.
Thats exactley what I did, I hooked up a rockford fosgate punch 40/40 amp. Its running to 12in. Kicker comp. Its sound good. The only problem when using line level converters, is that the factory radio automatically lowers the bass output when the volume is raised(thats to keep from blowing the factory speakers) So your never gonna get the serious(pure) bass you are looking for. But it is worth it. ;)