Precision M6600 AMD FirePro m 8900 Switchable GPUS with HD6970m Driver?

Well, I'm not familiar with the M6600, neither I am with the details regarding the chipset, I just thought it may be worth a try.
If by standard the IGP is deactivated in the M6600 it's unlikely to work. Maybe there's a hidden IGP setting in the BIOS which could be used if unlocked... don't know.

 

The IGP works with nvidia cards. It will not work with the IPS screen or AMD cards.

 

The inability to switch is based on hardware differences in how the video card signals are processed on the motherboard. You have to either go Nvidia or AMD on a motherboard - you can't have it both ways. Only way to do it is to offer two motherboards with two sets of licensing and twice the costs associated with making it all work and twice the time to get all of the certifications with software that Precisions are known for. This is not a video card bios thing. This is Nvidia and AMD competing with each other by having competing standards.