Hello to all, I just found your site through Google while trying to find a solution to this pathetic stereo system. I have the premium sound package in an 05 525i buy it has nothing for bass response. I would like to find a way to add a sub to the system without voiding my warranty. My dealership is really picky so this may have to be a removable solution as well. Where would I look in this site to see if someone else has already accomplished this?