Not going to get deeply involved here but perhaps I can add something that
will help...
There have been several reports of encountering similar audio issues while
rendering from storyboard only, and apparently, in those cases, the relative
files were composed of MJPEG encoded video and PCM audio (not the same as
MPEG... MJPEG is a hardware based video capture codec).
The problem was corrected by installing a reputable 3rd party MPEG decoder,
such as MainConcept MPEG or Ligos LSX-MPEG codecs (both offer free trial
downloads).
For some reason, MM2's Storyline appears to have problems rendering MJPEG
encoded content via directx, and, although I personally have not done the
in-depth research necessary to discern specific cause / effect, I am of the
opinion that the issue is directly related to faulty MPEG Splitter or
DeMultiplexer, which may not be fully dx compliant.
Anyhow, I must be off to fry other fish while the pan is still hot...