You could also try SPDIFer :
Spdifer | AC3Filter
More info on setting this and FFDSHOW up can be found here :
FFdshow Walkthrough: Basic, Intermediate, Advanced Configurations. - AVS Forum
That's what I'm using and it works fine.
Also, as this is my first post, I would like to thank all involved in creating and maintaining MP, it is an amazing piece of software!