The connection between the CD changer and DSP amp changed from digital to analog when BMW changed to the New Generation radios. The X5 got the New Gen radio in 2003; therefore your 2006 has the analog connection between the CDC and DSP amp.

The 100% comfirmation is that the coax SPDIF connection on your DSP amp is unused. If you had the digital audio connection, you would have a cable connected that runs to your Cd changer.

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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