These are the parts I used when I did my Sirius upgrade to my E38. I chose the SIR Mini antenna, because it is much less expensive and some think it has better reception than the BMW OE antenna. I would go with BMW's OE parts for the X5, which include the antenna mounting bracket, antenna, and antenna cable.

TERK SIR Mini Antenna
Sirius Receiver Module (Curren PN 65.12-0 416 377 comes with 1 yr Sirius subscription)
BM53 Radio Module (Current PN is 65.12-6 988 275)
Sirius to CD Changer Adapter Cable (PN 84.11-0 141 978)

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SOLD
2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input