Personally I have spent quite some time to find the best possible aftermarket Head Unit for my own M3. One criteria was that it should look as much as original as possible – however my demands to navigation, DAB radio, Dash and backup camera, Wi-Fi and more were not to be sacrificed. Quite a mouthful really. Nevertheless such unit exists. It’s the Avant 4 from AvinUSA.
I am presently installing the AVN4411PX610 model in my M3 so you will get the full stoy/documentation later. One thing, however, I can say right now is that the best way to route the 6m extension cable from the Head Unit to the trunk is out to the left under the dash board and along the left door sill. Explanations will come, but it’s clearly better than via the center console and under the driver seat.
I'll give you a link right away Avin Avant 4 for E46 M3. And NO, they haven't paid me to do so!
If you install a back camera, you need to get some wiring out in the trunk. SEE LINK
