Just A quick question. I'm looking at a Sabertooth 990FX. I'm curious because I'm looking at running 2 graphic cards unconfirmed yet but will be dual slots with a xonar stx and a daughter card for 5.1. Now my question is if I got one of these boards, could I use the bottom pcie x16 (runs at x8 if my research is correct) for the xonar stx and still run 2 graphic cards.
For the ASUS Xonar sound card you can use the PCIe 2.0 x16_4 slot which is the bottom (Dark Brown) PCIe slot, or you might be able to use the 3rd from top_ PCIe 2.0 x16_2 slot (Black) PCIe slot with the bridge over the top of it. Chances are you won't get x16/x16 with the GPUs. Ideally, find MOBO's with a top PCIe x1, above the GPU PCIe top slot, are best for sound cards, and in this case often the bottom PCIe slot for other PCIe cards (RAID, SSD, etc).
Refer to the manual on pages 2-15~2-16.
Q - What "and a daughter card for 5.1"?
If it's PCIe then see the (2) PCIe ports described above otherwise you'll have the older PCI slot to use.