Unfortunately if you want to go an OEM route there aren't many options. I recently fitted the Bang & Olufsen sound system from a F13 M6 (
https://www.2addicts.com/forums/show....php?t=1654382) into my car and the reason i did this is because i wanted a fully OEM but still good sound system.
What you can look at is the F30 Harmon Kardon sound system (it is different to the Harmon Kardon on the 2 series) and is very nice as well. Although this might be beyond the scope of a normal car audio shop as it requires in depth knowledge one BMW systems specifically and some custom wiring.