vautier

Just got a 1996 E34, 540i I've tried searching the forums but it's a mess of information and I can't quite find a clear answer The car currently has a Sony Xru550 head unit - i want to replace or modify it so I can have an aux input. Tape to aux sounds a bit crappy. what options are available for me? If there is a head unit that can essentially slot right in, that would be awesome, but I don't mind putting some time into it