I have full steering controls and rear parking sensors. The harness was supplied by the installer so i can't tell you the make, but this was over £100 to ensure everything works.
Rear parking sensors now beep from the front behind the head unit and don't sounds as good as original, but work as before.
I now have full ipod control through steering wheel which is nice.
I did think about a double din, but this was further bumping up the price and the sound quality would not be as good.
E90 330i SE Auto Graphite Grey Metalic