Not sure how to tell if they're 16 vs 24 bit. I normally go off of this
http://grimwiki.net/wiki/Custom_Sound_Tutorial for creating the sounds. What is unclear is if you have to have 44100 sample rates or if it can be smaller (8000 for instance). All are saved as mono, 16-bit PCM wavs by Audacity (using 2.02), including now the last two I didn't catch before.
[Edit]
Can determine the wav format via the 'file' command (in my case from mingw/msys). All are 16-bit, except 4 which are 8-bit. Do 8-bit wavs work? One of the wavs in the sx_fountain package is also at a 48000 sample rate, but stored mono 16-bit. Do the sx_fountains sounds work at the higher sample rate?