Two 1070s on a single Win 2008 R2 node? Win 2008 R2 will boot with 2,4,6 GPUs but not 8

I have four of the NVidia interface cards in a Windows 2008 R2 server. If I connect 3 of the cables, the system boots, and all sixe GPUs are active. If I connect all four cables, the system stops after the Windows status bar.

I have disabled the onboard NIC, RAID and any other PCIe devices. Neither the 197.03 or 197.45 drivers will work.

This used to work with Windows 2008 server.

Any ideas?