Checked the Mic - its definately passive.
It looks like the Fiscon Mic made for inside the light fitting is our only option... but I'm a bit dubious if it will make the call quality any better than the standard one since its the same Mic inside a plastic housing 
I knew it was passive and that the active VW OEM microphone would blow the FISCON electronics due to its greater output. Could not FISCON design their product with an active microphone?
The FISCON Bluetooth is a Parrot affair which employs a passive microphone. I suppose this sort of configuration is easier to use with a variety of aftermarket systems. The Parrot system is also used by Pioneer and Kenwood.
I only wish the VW Bluetooth preparation was compatible with the iPhone and the BlacKberry.
Erik had a problem with the VW setup and its incompatibility with his iPhone. So he had to buy a Nokia smart phone in addition!
I have been told that with the passive FISCON microphone in the light housing, the sound quality is not very good, as this microphone is not an active directional microphone.
This is becomming a real pain.
One thing I am sure of: I don't wish to have the microphone hanging from the 'A' pillar.
And now, I really don't know how to proceed and I am also desperate to get a Sat Nav installed.

PS: Maybe your electronics engineer could use some series resistance to reduce the output from the OEM microphone so that it is compatible with the FISCON. He can measure the voltage from the passive microphone for a 60 dB SPL input and adjust the output of the OEM active microphone accordingly. He can also measure the input sensitivity of the FISCON device and then enable the OEM microhone to be compatible with it.
Oh, deary, deary me!