All, I signed up to the forums mostly just to say THANK YOU for this invaluable information. I am building a new studio with a new Mac Pro and a DM4800 with the IFFWDMmkII card, and have been fighting it for several hours until I came across this thread. Unfortunately, I did not see this until I had already installed OS 10.10, so I am in the (somewhat painful) process of wiping the boot disk and starting over with 10.9.2. It sounds like I am safe to go to 10.9.5, but I will stop there for now.
Thanks again!
Russ