Good news - you're a MY03 Business CD and 100% compatible for AUX and Sirius. Here's a shoping list of what is needed:
Sirius Satellite Radio - e53 X5
http://www.europeanautosource.com/pr...roducts_id=274
Nothing else is needed - even 12 months of programming comes bundled with the Sirius package along with full instructions.
And your AUX kit:
Auxiliary Audio Input - e39/X3/X5 Business CD
http://www.europeanautosource.com/pr...roducts_id=297
Full instructions included as well.
Only MY05 X5s had MP3 capabilities, but you would be
much better off going with a DICE and iPod for MP3 playback. Going this route will give you steering wheel control, charging and text display on your Business CD display and is 100% compatible with Sirius. If you go the DICE route, you can eliminate the BMW AUX portion since this is already integrated within the DICE:
DICE iPod Integration Kit for BMW
http://www.europeanautosource.com/pr...roducts_id=268
Let me know if you have any further questions, we're here to help.