The basslink is good for fill-in bass. Its one of the better self-powered/enclosed subwoofer systems. I would suggest breaking out the center ski boot.
If you fold down your rear seat center armrest and peel back the leather flap you will expose the metal plate where the ski boot is. BMW fabricated this so I can be easily popped out with a little force. This will allow sound pressure from inside the trunk to enter the cabin.
Greg Mannino
Car Audio.Video.Security.Navigation Guru
Electrical/Mechanical Specialist