I am not sure if what I have called the 'shutter' is even a shutter. I just used that term because it is mentioned on the e90 xenon retrofit pages. Wire 5 on the xenon headlamp seems to be for a dipping mechanism (see photo)
I think what I will do is install the lights when I get the obdII cable and inpa/ncs expert, then code it to xenon and see what happens. I would assume that the footwell module would use the low beam wire for high beam also. Or failing that, tap the high beam and low beam wires.
Hopefully someone who has actually got this to work will fill us in on what we have to do.