Yes, Sirius will work fine. The nav computer's setting has no bearing on the radio and Sirius module. I have run my Sirius module with the nav in both US and Euro mode.

Now, your BM53 radio needs to be in USA mode to work.

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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