slitaz-3.0.iso and slitaz-3.0-firefox.iso are both missing aplay, even though the alsa-utils-1.0.21.tazpkg is preinstalled. You can grab it from a fresh download of the alsa-utils package. Since tazpkg will complain that it's already installed, just unpack the package, and copy aplay manually into /usr/bin.

Not very important, I know. But arecord, which is already there, is a symlink to aplay, so without it the symlink is broken.