converting m4a (aac) to wav

[jacobacci]

I am trying to convert local m4a (aac) files to wav. Minimstreamer is installed, as is ffmpeg.
The files were created using qaac, so they should be genuine apple aac files (with extension m4a). I put aac:wav into the stream.properties field.
When I stream these (local) files to the dlna renderer, no conversion happens. The renderer reports aac.
Putting m4a:wav into stream.properties results in illegal media type.
Do I have to rename all files from m4a to aac?