I have used madxlib successfully to convert from MP3 to WAV and MP3 to PCM which was burned to cd with imapi (all in vb.net). It looks like aumplib does even more. Madxlib was quite tricky to use - to get the dll I needed C++ express, and I think I needed to stick a WAV header onto the top of the file. If there is an easier option available then use it!