After an hour or two spent troubleshooting today, it has become clear that either our DVD player or our receiver has developed a fault. Everything works perfectly except DVDs, but while DVD video displays perfectly, we're getting no audio when playing DVDs except for (under the right combination of settings) the subwoofer track.
I am so TIRED of things breaking that we can't afford to replace or get repaired.
(And I just discovered something really weird .... can anyone think of any reason why hitting Ctrl-Alt-P, in an application window that has it bound to a function -- this LogJam window, actually -- should cause a Slackware Linux box running AccelX 6.1 and fvwm-2.4.17 to switch to an unused virtual console that doesn't have a getty running on it? It is not to my knowledge bound anywhere else; certainly I don't have it bound to anything in fvwm.)