Hi 24c,
I have the very same early 2011 MBP with the same VGA cards but when I installed the Bootcamp drivers on the windows 8.1 the screen blacked out and I had to delete the Radeon drivers in safe mode to have picture plus sound is not working at all . What version of windows do you have and what kind of drivers are you using? I decided to switch to parallels even though a virtual windows is weaker, do you think my Einscan gona work on parallels? thanks