If you open the file that you think the sound files are in you should see several files that represent the various altitudes you should be able to click on them and hear the appropriate sound.
at the bottom of the file there should be a sound.cfg file
if none of these are there than that is why you do not hear them.
You also should have something inside of the aircraft.cfg file for the plane that will use these sounds
it should be in a section labeled [GPWS]
Look at the default B737-800 aircraft.cfg file for an example it is at the end of the file