Scan only for *.aiff files
Currently, all files in /System/Library/Sounds are selected and added to the sound selection box (after stripping their extension). This would also include .aif files. However, when sounds are played, the .aiff (with two "f") extension is added and thus, aif-files cannot be played.
Solution: Only add files matching /System/Library/Sounds/*.aiff to the list.