How Do I Add 2nd Sub?
 

If I wanted to add a 2nd aftermarket sub to my X5 where would I need to tap into?

Well, if your going to add a second aftermarket subwoofer, you should be looking at what you have currently - it's not recommended to mix and match subwoofers.

Aimster, if I remember correctly, you have the Basslink, correct? Are you looking to add another? If so, you would simply tap into the same wires you've already tapped into for your source signal.