Strangely these two boards do not have anything different in their microcodes ie. They both have identical entries. The only CPU support related difference i could find was the AMD AGESA Version in each one. The bios must have AGESA v3.6.6.0 to identify X6 CPU's , which the F8 board you linked to had but the F11 version of your own board didnt (It had v3.5.3.1) so ive upgraded the AGESA to v3.6.6.0
Try throwing in an X6 now to see if it takes it (Seeing as thats why the new AGESA version was released that may all that needs to be done)