Reddit has an elegant solution to the sound issue. Simply convert .mp3 files to .wav files. The .mp3 files in the TWS sound directory can be manipulated this way:
ffmpeg -i FILE.mp3 -acodec pcm_s16le -ar 44100 FILE.wav # or as a oneliner for all at once find . -iname '*.mp3' -exec sh -c 'ffmpeg -i $1 -acodec pcm_s16le -ar 44100 $1.wav' sh {} ';'
The sounds directory has voice based sounds. For the actual sound oriented sounds, you'll need to supply your own, or pull from the original distribution and convert. An example extraction from the article:
jar xf ~/Jts/1019/jars/jts4launch-1019.jar $(jar tf ~/Jts/1019/jars/jts4launch-1019.jar | grep '\.mp3$')
Note 1: In the Sound Manager, prior to selecting the .wave files, you may need to switch between 'voice' and 'non-voice' profile. Mine is currently: 'non-voice - modified'. I then selected the .wav files. But refer to Note 2 for what might be the real mechanism.
Note 2: Also, the sound mixer does not seem to come into play, ie, no other sound source can be operating.