It was surprisingly easy to get CasterSoundboard working on FreeSlack, or Slackware.
When I installed FreeSlack, I installed everything as recommended, like KDE and Xfce. The compilation of CasterSoundboard was instant.
I have all the sounds. Now, all I need is a way to connect CasterSoundboard to Mumble.
Also, CasterSoundboard seems biased toward the QWERTY keyboard layout. I hope it detects one's keybard layout so the map is not scrambled for Dvorak users. If not, I might have to patch it, and I don't want to do that.