Well, despite some manufacturers claims that a FX will work on some 8XX chipset with just a Bios update, I wouldn't botter trying.. isgust;
My advice: get a 9XX chipset motherboard for that FX, or get another PII X4/X6 for that mobo..
I had read all kind of scenarios with a 8XX chipset+FX.. Some works just great, some are a pain in the arss..
But, as you describe your problem, it must be a compatibility issue due to the Bios.. Neither is faulty, just don't match as it should..
What to do??.. Get a new CPU/mobo to match each, or talk to the Asus people and see what they have to say about it..
8320 @ 4,7 / 990FXA UD5 / CF-X 7970 + 7950 / Switch 810 / H110 p-p / 16 GB RAM / 23" 5760x1080 / SSD 64GB RAID0 / HX750 / SB Recon3D Fatal1ty Champion / z506