We are doing this to a 2010 135I. Adding a Helix Pro DSP and an amp. We are picking up the signal at the speaker leads and going into the helix high level. You should also be able to do this if you have the basic BMW system. Go into the amp high level if it has that option. The 5 series we have at the shop had an optical output and we used a mo-bridge to a helix c-dsp then to the amps. The only concern we have at this point is if the factory head unit has a x-over and will not give us a full range signal. We will find out very soon if that is the case. With this basic install we will not have to get into the dash, so there will be nothing disturbed behind the factory head unit. Hope this helps.