I put in a pretty hefty size amp (5ch) to run 8 speakers and a sub in my 92 conbrio/impulse. Didn't upgrade alternator and have had no problems, but have noticed that my volt gauge sets lower than it did prior. I will be upgrading mine over the winter, as I also plan to add another amp and 2nd battery dedicated to the stereo.

DB electrical has the best prices I have seen so far on upgrades.