thanks for your reply!
The cards do not show up either in windows or in OSX Lion with the X9DAi. They do work on my other computer which is a 2008 MacPro. So they are not broken.
Are there any options in the BIOS i should try out?
To answer your other question: The system works quite well as a hackintosh. Very stable. However, Cinebench seems to be around 25% faster in Windows7. Probably because the turboboost option is not yet supported. I am curious if it will increase in 10.8
I built the system to work as a hackintosh because I was frustrated with the last "update" of the MacPro. I was waiting for 2 years for a real update and it did not happen. As I worked on mac computers since the beginning of my carreer I am still having some trouble converting to windows. Thats why I wanted a system that works in both worlds...
Anyways, I am very puzzled about those hardware issues which do not seem to work. Because I do not know PCs and Windows well enough to find out if there is something wrong with the hardware or if I am just doing something wrong.
The weird thing really is that the graphics card works well in every slot, but the cards dont. And I know that the cards are not broken....