Yes, all that is on the I-Bus. The key is that I-Bus communicaions is not general broadcast. Instructions are directed to specific devices. So, most likely, the in-dash radio is not directing anything to the nav computer. Others have tried it, and it did not work. The best I can say is give it a try and see what happens.

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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