Xmosaic is generally a way-cool program, but it does need one local X resource tweak. Fortunately, Xmosaic uses X resources (see here for a dense man page that talks in part about X resources) to set things up to play audio files.
Below, there's really only one Xresource that has to be changed locally:
OR
There are two Xresources that may need to be used, depending on how your path is set up:
Hope this helps...