Ok I had this beast at my place today.
The owner wanted Kufatec kit installed and wanted everything in stealth mode
. It was mentioned to him that hiding aerials may impede TV signals but he wanted to give it a try.
Also I wanted to experiment and hide the TV box behind the glove box if wirings would allow me.
It amazed me that M3 has no airbags in the front side pillars. Good sign so that I can hide the aerials in those pillars.
Fitting aerials in side pillars
Media box hidden behind the glove box and USB extension cable used.
And final results after coding (owner saved the money which would cost him to buy drive in motion unlocking kit)
Yes signals get blocked if you try to hide them in the side pillars. TV freezes when you are travelling next to tall buildings / trees / bridges.
However owner preferred stealth mode over signal loss, so aerials were left in the side pillars.
Overall good results!