AFAIK CoreAVC has nothing to do with audio. FFDSHOW can be configured to process all (uncompressed) audio flowing through DirectShow. So the usual question: What filters are displayed when you click
Options -> Filters -> Advanced ? (it's the filters & DirectShow usually doing the job, not BSPlayer)
Do other DirectShow applications output audio properly?
Do other standalone applications like Winamp or Foobar2000 output audio properly?