just a friendly suggestion - if you are keeping the car and replacing the audio components, you'll want to hold onto the factory amp.
if and when bmw needs to reinstall the software in your car, which is a step in diagnosing various issues, the factory amp /must/ to be connected to the MOST bus for the software to be installed. I am not sure if sirius is included in this requirement. I didn't remove mine. you could ask on the thread below, others probably know.
I wasn't aware of this, until I had a recent issue with my turbo's, but I had held onto my factory amp.
http://www.e90post.com/forums/showthread.php?t=791030