I am using an Asrock Z87 Extreme9/ac connected to an Apple Thunderbolt display. I use 2 Sapphire HD7970 connected via Crossfire. The output from the discrete graphics is connected to the displayport input and output to the Thunderbolt display via a Thunderbolt port. The system works, but there is no display until the operating system (OSX or Windows 7 64) loads. Everything then works properly, but there is no way to see or change the bios settings. If I physically remove the two graphics cards, the IGPU will provide video to the Thunderbolt display and allow me to see the bios.

Is there any way I can display bios information via Thunderbolt using the pcie cards as the primary display?