A little update concerning the new style MMI boxes that are now being supplied.
I'm told that amongst the new way to connect it that they don't come with the adaptor loom to tap into your existing microphone. So I've put my thinking cap on and come up with this (** please note I do need to actually test this to make sure 100% that it will actually work but I'm very confident!)
So you need to buy one of these 3 pol Y looms from eBay...
Now you need the male and one of the female plugs to connect with your existing microphone plug.
You then have an option as to what to do with the other end...
1) You can cut off the black plug on the loom...

and then buy one of these 3pol plugs (with new crimps)...

and attach it so it just plugs into the new Y loom. Yellow wire to pin 1 and black wire to pin 2. Pin 3 is not used.
Or
2) Cut a length of the supplied microphone wire (with the black plug attached)...

cut off one of the female plugs on the new Y loom...

and then solder the white wire to the wire from pin 1 of the Y loom (Yellow in these photos but colours may vary depending on supplier) and the braid to the wire from pin 2 (again colours may change but green with yellow stripe here). Don't forget to heatshrink your soldering.
Pin 3 wire is not used in this instance.
So you should now have an adaptor loom for your existing microphone. In some options there can be two microphones, I chose the left one as this is the one that goes to the Combox or MULF and is used for Bluetooth calls etc.
I'm going to make one of these up with the bits and pieces I have laying around and test it on my (older) MMI box I have installed using method 2 above, that way I can use the black plug that fits the supplied microphone (with the older boxes you had two choices!).
I'll report back just as soon as I can.