Actually, I was thinking about getting an aftermarket sub and amp but I want to keep the car original as much as possible. If I bring it to some place for sound set up, I'm afraid I might get lots of squeeks because the panels are not put back properly.

I've already experienced it in my other car. i brought it to one of the top sound system installers in the country. But after getting the car back, I hear squeeks at some panel. Don't want to have that in my X5