Hi Jsnow,

Regarding this:

ATI Radeon HD 4850

• worked neither as primary nor secondary (BSOD atikmdag.sys)

  
  

I had this happen once upon initial passthrough of my ATI HD 3450.  Try the following:

1.     if your ATI card also has the HDMI audio, pass it through as well, just until you get the catalyst driver installed - it can then be removed again

2.     Remove any other passed through devices to the vm temporarily

3.     This BSOD is a known issue with the 11.6 driver in general (from what ive read online, so its not necessarly being caused by passthrough)

4.     Boot into safe mode, disable the ATI card in device manager, reboot normally, re-enable the card, then try installing the catalyst driver again

Good luck!

BAM.