First a couple quick confirmations: There is an orange LED near the left radio/volume knob to indicate when the radio is on. Does that LED ever turn on? I assume from your initial description that you can not get a radio view to come up no matter what you do, right?

If you never get the radio view and you can not get the orange LED to turn on, then most likely, your problem is a dead radio module. The radio module is the silver module next to the battery in the tire well.

If the radio view came up, but no sound, then your problem would likely be the DSP amp.

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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