If I remember correctly BBT started with p106's and started adding normal GPU's to max it out instead of the other way around.  I would check the latest BIOS/chipset drivers for updates on compatibilty, but 8 normal Nvidia and 8 amd should work fine, or start with 13 AMD and add Nvidia one at a time.  The worst part of that board is the crazy loading times and then trying to load OC values after that.  Seems more feasible to stick with 8-13 GPU motherboards.