BMW IBUS steering wheel controls can be used both for car PC and BMW OEM stereo with CarPC JoyCon Exd. (BMW E39 E46 E45 E38 E36 E37 E38(Z3) E53 E83)
You do not need to give up BMW OEM stereo for car PC.
You can preserve the steering wheel controller’s original function(radio control, vol+/-, seek up/dn and so on) with BSGd. BSGd is supported by CarPC JoyCon Exd itself. No additional device is required.
User Guide of CarPC JoyCon Exd
https://www.exinterface.com/d/man/cpjexd/CarPC_JoyCon_Exd_UserGuide_eng.pdf
You can switch between BMW stereo and car PC like Windows applications.