I bit the bullet and went out and bought a 7750, initially had the same problem, then I uninstalled the device and re-detected it and installed the drivers, and windows still refused to start it saying something about unsigned drivers.
So I un-installed and re-installed again, and windows now detects both displays, however whenever I try to switch to the passthrough 7750, I ge the BSOD.
I have tried both options to use the new device as the display and "Extend These Displays" - both result in the BSOD.
I don't seem to be having much luck !
