Guys, I got it working ;-)
with the 6600GT you have to use a DVI-to-VGA-Adapter to get both outputs work. Additional this this you have to backup your VGA-Bios (by NVFlash) and use NVCAP-Generator. Then you have to include the NVCAP-value in the info.plist of your kext (I recommend NVInject.kext).
I will show you mine ;-)

Greetings,
-crawle