I'm driving my 2007 X on long trips these days and would like to listen to my classical music CD's or maybe put in Sirius. My Rockford Fosgate stock system is pretty good but I'm wondering if it could be improved by replacing the 8 in-door and dash speakers with better quality aftermarket units? This means keeping the Rockford head unit and the subwoofer. Any experts out there who can advise me? Will I get cleaner sound or - waste of money?