Same issue here with my new z97X-Gaming 7 built today.
No sound and all sorts of wierd issues trying to resolve it through sound properties.
I uninstalled the realtek driver and the XFI software as "mtheonethat" suggested above and immediately got sound.
I could not see where to download the latest version of both those files in the app centre though, so I got the realtek driver from
http://www.gigabyte.us/products/product-page.aspx?pid=4959&dl=1&RWD=0#driverinstalled it
then installed the XFI software off the CD that came with the mobo.
Now it's all good.
Spent over an hour trying to figure this out before seeing the above post - thanks a lot for posting the info.
As suggested above it is important to do it in that order, and the download page linked above does state that.