Almost all decent boards are now equipment with pretty good onboard sound. Some descreate sound cards like Soundblaster X-fi etc offer some additional features and can also offload some effects processing. The Realtek on-board chip in your case is decent, although you may notice some differnce when compared to the X-fi. Personally I'm moving over my old X-fi for my new box.
I'm building almost the same thing you are, going with an OCZ Revo and an ASUS board though. Check out the board below, I've had probably 8 ASUS boards over the years, no problems, the one GB board I had LITERALLY melted and charred the board, components dripped off. In all fairness I sent it back and they REPAIRED IT (the board still had the char marks but they resoldiered everything and it amazingly worked), but since then I've always stuck with ASUS.