We have not had similar cases reported nor do we have a known issue with 16x PCIe* video cards. Unfortunately, we do not have a tested graphics card list that I can share with you. Generally, as long as the PCI Express* card complies with the PCI Express* Technology, it should work; for further details on this technology, please, refer to the following URL:
You could also double-check with the video card manufacturer to see if they have a desktop board compatibility list of their own.
You could alternatively test with the most current BIOS version (Click here). Once the update is done, please, restart the system into BIOS and proceed as follows:
Press <F9> to restore BIOS default settings. Reset any customized BIOS settings. Clear all DMI event logs by setting the option to "Enable", which is located in the Advanced/Event Log Configuration section of the BIOS Setup utility. Press <F10> to save the new settings and reboot the system.