I currently did same Bios with 9 cards and it's running stable.

Here is what I changed to get more cards registered:
-Update bios
-DMI Max Link Speed [Auto]->[Gen2]
-PCIEX16_1 Link Speed [Auto]->[Gen2]
-PCIEX16_2 Link Speed [Auto]->[Gen2]
PCIe Speed [Auto]->[Gen2]
HD Audio Controller [Enabled]->[Disabled] (Not sure if this actually has anything to do with getting cards running)
Above 4G Decoding [Disabled]->[Enabled]


All the above can be found in the Advanced setup of the bios. Except for Above 4G Decoding which is in boot menu of bios.   


Hope this helps.