If it is of any interest I have just installed Yosemite 10.10.2 with no problems using the modified DSDT and Audio kext that I posted above.
Audio works - have not tested much else yet.
I now have instances of Snow Leopard, Lion, Mountain Lion and Yosemite all running on this board.
It might be old - but it works (a bit like me, I suppose !)
Wow this is awesome. I still have this board with regular Lion installed from an upgrade of Snow.
I'd love to get it updated to Yosemite. What do you think is the best route? Upgrade of start fresh?
I'd love to compare notes. Do you have any special BIOS flashed on yours? If I remember I had to flash a certain BIOS as well.