The MP3 adapters tend to provide a little more resistance, and the head unit sees it as the end of hte tape, and keeps changing the side from 1 to 2, and it never really plays. My Taurus would do the same thing. The JBL (a little more power but not much more and a small subwoofer) will sound similar to yours, about the only thing you can do to make it sound a little better is turn the bass and treble all the way up, that makes a Ford system sound a little better, but for real upgrade for the best value, find a $100 Pioneer and slip it in there. I put one in with a jack on teh front to plug my MP3 into, and it works awesome...