MOST Fibre optic interface to allow the fitting of a new head unit into a BMW  with the TOP HI FI SYSTEM (Logic 7/ Harman Kardon) original audio and retain the use of the fibre optic amplifier. You will lose front to rear fading ability.

if the car has speaker wiring in the  Quadlock connector  then it is NOT a fibre-optic amplified system and this interface is not needed.

This interface does not retain the use of the steering wheel controls.You should use separate steering control interfaces  49-BMW  for Mercedes cars