Late reply but I figured out that if you don't have blank line between decoding periods checked there is no audio alerting. Try that.
In addition to moving the sound files, I had to rebuild to be able to debug everything but the problem is the audio alerts are tied to the "blank line between decoding periods" -- if you have that off, no audio alerts. If you turn it on, works fine.
Thanks for the great work. The .deb file installs sounds at /home/uwe/sounds (my user name is NOT uwe -- it created this directory). After moving that directory to my ~, sounds still not working -- investigating that -- but the installer should probably put them at /usr/share/JTDX/sounds anyway.