watman: -Also your long shot disable Speedstep suggestion may have worked, haven't had any audio stuttering yet, but it may take a few hours/days of watching mindless TV to try to replicate the problem
-Side question, the Speedstep, what will the effect be on the performance, if any, due to being a HTPC?
Speedstep is a power-saving function which slows down the CPU when it decides that full clock speed is not needed. In your case, it's possible this could be kicking in after a while due to the 10% CPU usage while playing video.
Basically, the power saving is minimal at best, so I would always disable it where you want the best performance from your system.
Speedstep is usually of more benefit for a laptop rather than a desktop PC.