As a follow-up to this I came across a hack somewhere which seems to be working on my setup.
Pin 19 of the hdmi cable is a hot-plug signal carrier.
So to test I've simply put a slip of insulating tape over it before inserting it.
First I used moninfo to create an inf file for my avr (pioneer vsx-2020) and set windows (v7) to use it.
Had to start then shut down then start the computer again and since that all is well.
No more xbmc crashes and continued audio etc when turning off the tv, projector, changing input on the avr or even turning off the avr
Some people may find the the need to pull-up pin 19 to 5v using a 1k resistor to pin 18?
The original forum is here http://social.technet.microsoft.com/Foru...80a21fdc2/
Its quite long and has been going on for years - way to go microsoft!