Avin4 head unit is only $370, and you already spent $50 and may be more in your quest, eventually adding up-to close to the $370 for the Avin4.

https://avinusa.com/avant-4-multimed...mw-x5-e53.html

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'05 E53 X5 4.4i, '97 E39 528, '07 E92 335i, '16 F86 X6M.