I caved.....I bought a second hand set of buttons off ebay and BINGO!
The MMI popped up and worked PERFECTLY
I could see 07 control head in VCDS and ODB11 auto-coded everything back as working!
SO if your MMI pops up for ~5 secs then drops, VCDS optical test shows everything working (Optical+Electrical) and your buttons are un-responsive, it probably is your buttons.
The idea of disconnecting the buttons and your MMI will still work is absolute bobbins. For *some* reason the control head needs to see the buttons to work - Certainly on my 05 D3
More details of my journey on:
http://forum.a8parts.co.uk/showthread.php?t=16341
http://forum.a8parts.co.uk/showthread.php?t=16352