Yes. As long as the motherboard has a PCIe x16 slot, which basically every motherboard from the past decade does, then you're perfectly fine. (And yes, yours does.)
As for the sound card, that depends on the sound card - there is a PCIe x1 slot down at the bottom, if you don't get one of the GTX 780s that has a ridiculously large cooler. That being said, though, there's really not much need for a sound card anymore unless your computer is plugged directly into a very fancy sound system... that for some reason doesn't have a DAC built into its amplifier.