There seems to be something quite serious in this board with regards to grounding. I think that is what causes the "FF". Probably the plastic used in the motherboard is not rigid enough and thus you get "bends" when both processors are connected. Even when you install the backplates you can see some bending. On the Intel D5400XS I was a little worried with that when I used a dual vapor setup using very large vapor and heavy vapor heads, but even with obvious bends I would never get instability or funny clicking sounds when I tightened the nuts on the vapor heads. What seems to happen on the Asus is that after you use it for some time, heat somehow allows more bend or the expansion caused by heat causes something to expand which causes a short or some sort of interference that causes "FF". Somehow removing both processors and all memory seems to "clear" this short and once you install the system again it seems OK for a while.

While I simply don't have the time to trouble shoot this board I would advice anyone who is installing such a system from scratch to be gentle with the tightening screws of the HSF. Also I would advice to protect the underside under the CPU's with plastic tape to reduce possible build up of amps from the steel bracket that could be causing intereference. I still have about a week before I get my D5400XS so maybe this weekend I will try a few more things to revive this motherboard. But really this is way too much trouble than it is worth, especially since there are excellent alternatives out there. To anyone planning on building an Octa I would highly recommend the D5400XS. I guarantee that with E5430's you will get 3.2Ghz by simply running the memory at 400 Mhz and increasing by one or two micro notches the voltage in the BIOS. I have such a system running 24/7 at full load now for almost 4 months with not a single problem. For cooling I used two extra Blue Orb's I had lying around, so no need for expensive special HSF cooling. The only problem is that the board is huge and you have to look hard to find a case that will fit the board.