ok i want this to be the last time i say this since people dont seem to be reading the posts. you dont need to change the lua code to play what you want, just go to your sounds folder in your gmod directory and replace the current sound file wth your own. this requires no lua changing whatsoever but you can if you want, but thats server side, all its doing is looking for the sound file named lasthuman in your directory and playing it.
i think for random server's zs you need to name it lasthuman_test