So I finally upgraded my AUX installation to Bluetooth!
I simply purchased a Bluetooth Adapter for the E60 (25€) and connected it where the AUX cable was connected before. Additionally, I had to get power and mass. As I tapped into that already while installing my rear view cam I just applied my rudimental soldering skills at that same location again.
Since I had AUX already coded, Bluetooth was plug&play and everything worked immediately.
I know can listen to Spotify via my phone.
Only downside: I’ll have to work on my CarPC again in order to get Bluetooth up and running on the Raspberry Pi as well.