Keep us all posted, It looks like a cool upgrade! and cooler if it improves reception!
Ive read that the shark fin has 4/5 antennae in there, (satellite radio, Bluetooth, GPS and regular AM/FM ?? )
good luck!! (post part numbers etc too please!!)

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2003 X5 3.0i (02/2003) sport package, Sapphire black metallic / Black Dakota Sport seats. compass mirror retrofit, trailer hitch retrofit, Prodigy P2 trailer brake controller installed, PDC retrofit, Lumbar support retrofit. heated rear seats retrofitted. Running boards retrofitted and subwoofer install in progress. 4.8is Brakes installed front and back. Bluetooth TCU installed, Rear Fog lights installed. Retrofitted reclining rear seat backs.