Are you using the Ouya marketplace version of xbmc? If so try the previous version and side load it, or be brave and try the monthly of 13.
I also had an issue such as yours with sound, a quick Google led me to believe it was xbmc causing it. I run ISO's primarily so I needed the non-ouya store version anyways and have not had a sound problem since. Hardly conclusive, but I have not had a sound issue since so I did not dig into it further.