I have Studio HD 15. Like many others, my sound didn't work in the program. After trying all the fixes with mixer settings, volume control, etc...I found a fix for something else that peaked my interest.
Most modern motherboards in PC's today have on-board sound. Most video cards today also have sound hardware for HD sound output though their HDMI ports as well. That means a PC that has a motherboard (all of them), a video card, and a sound card can have 3 different hardware sound solutions in them.
So why is this important ? I found a simple fix from AVID to get sound to work in Studio HD for systems with multiple sound cards (even though the common thought would be I have the one Xonar STX card installed).
I implemented the fix, and voila...my Pinnacle StudioHD program has sound again. Here's a link to AVID's fix... No audio preview when multiple audio cards are installed