Any idea on installing an after market HU for E39
 

my stock nav was broken long time ago, using a portable gps, it allows me play music while navigating, but you cant expect too much on the sound quality, so i rarely use it to listen musics, i'm kinda tired of hearing boring engine sound while driving alone, plus i have to keep charging it with cigarette charger, the wire out there looks ugly, so i 'm planning to install an aftermarket headunit, any advice will be appreciated.