This is even weirder. Despite the warning, I continue to hear sounds when I open and close windows (for example). However, when I hit the "Test Sound" button in the KDE control center, all is silence. I've fiddled with the mixer, but it hasn't made any difference. Also, the fact that there is something to mix is probably signficant, since when things go really wrong there isn't. Also, I'm using devfs.