Harry,

I have Parallels and not put Windows 8.1 on the desktop yet, but the drivers for BootCamp come with the Apple BootCamp install. I never needed to use the AMD Radeon control panel, just the Displays Control Panel was sufficient, as you just need to set the second display to 800x600 to drive the Einscan projector. The Pro version of Parallels is supposed to have a few enhancements that I believe the Einscan looks for in a Windows install, but the new release of VMWare Fusion 10? might have these too.

I'm also like Hugues, but I'm using an Early 2011 17" MacBook Pro, running under BootCamp.

Mike
PS Parallels, normally sorts all the stock drivers out to work in Windows with their install. So when you plug in your Mini Display Post VGA adaptor into your Thunderbolt port hooked up to the Einscan, it should ask you which OS you want to use, so you just hold down the Alt key and click over Windows, that way everytime you start it up, Parallels will boot up.