I have the Asus Rampage Extreme IV and the onboard sound is superb coming from my Intel Skulltrail.
I was using Astro A40 but since Astro screwed me with 2 pairs off A50 wireless that arrived dead out the box, and then a further dead 2013 mix amp i moved away from them and bought a pair off Roccat Kave true 5.1 headphones.
I was looking at getting a Phoebus sound card but now that Roccat are going to be releasing their new Kave KTD with USB sound card I'm not sure what to do.
http://www.roccat.org/Products/Gaming-Sound/ROCCAT-Kave-XTD/The Kave KTD has a nice feature to answer your cell through the game headset which could be quite handy as most times i just ignore who ever is calling me during a game.
As for the the mouse, i have the Logitech G700 and its been great the past few years but now the right click is funky, doesn't always work (many deaths trying to get the scope up to shoot and nothing happens).
I was looking at the Asus GX1000 vs one off the new Logitech either G602 or G700s. Not a fan off wireless gaming mouse but with the G700 (possibly G700s) it's optional if you use wireless or leave the usb charge cord plugged in.
If anyone else could sugest a good mouse or thought's about sound card/headset for 5.1+ gaming i'd love to hear from you.