I know absolutely nothing about car stereos - I've always been one to use all factory stuff. But I really want to upgrade the system in my car now. I have a 2003 Chrysler 300M. I'd like to keep using the factory head unit, because it is has integrated controls on my steering wheel, and I don't want to go for that gaudy look of aftermarket systems. So my plan is to get a four channel amp, and upgrade all the speakers (6x9's in the back, 6.5's plus tweeters in the front.) I'm not gonna do the install myself. Any suggestions? Should I go to a big box store like Best Buy to have them do everything, or a specialty shop? Any specific brands I that I should check out?