The /tmp/file.wav was a typo, I was using the path with the full drive name:C:/tmp/file.wav.
In regards to customizing the SoundControl extension, I had previously tried to work with this extension but was getting an error (Breach warning, Open Sound Control, test with Pure Data errors) which i belive is related to purr-data.
Also, the use of Qt in python would require some form of C++ wrapping would it not? I know that the PyQT provides binding for Qt but I am not sure if I would be able to use this within Slicer.