I don't know if any of y'all have heard of this place, but i saw an add for it in a magazine and it looks pretty cool. The company is called Bavarian SoundWerks and specializes in BMW Audio. Thy hace complete simple speaker replacement packages that they recommend and seel as a kit depending on your music style. They have custom BMW specific subwoofer systms that are easily installed and are perfect matches. (the custom one they have in the add looks super clean and really nice) they Have ultra-Lightweight subwoofer enclosures built specifically for BMW''s their lightest one is 19lbs while other companies boxes start at around 45lbs.
I know this should go in the elect5ronics section but a lot of people on the forum could benefit from this thread and put it here so it's easily seen. I don't care if it gets moved later