Again, there's still no need to make it an addon. Make the S65 sound an addon and leave the schafter3 sound where it is. change the audiohashname of your c63 to SCHAFTER3 and the audiohashname under schafter3 to whatever your S65 sound is called.
Just create a dlcpack that contains the audio files for the s65, if need be, take another addon pack that has audio, rename all the references to the dlc in all files, and remove everything that isn't the audio file.