Hi there,
I'm a Win32 C++ developer and have used DirectX many times, usually on camera and audio/video related projects.
Should be able to provide you with this Filter Graph, once I look in to it in detail and remember PCM codecs etc.
If you send me the sample AVI files, the codec that needs installing etc, I can get to work on a quickly-put-together test command-line .EXE?
Let me know.