Software :: Sound Fails In SOME Applications Until Reboot?

I am having a HARD, PARTIAL FAILURE OF SOUND on my Linux system (Slackware 13.1, the latest, with a 2.6.33.4-smp kernel and KDE 4.4.3). The failure is "HARD" in the sense that once it occurs it remains broken until I reboot the system. It's a "PARTIAL" failure in that it affects ONLY SOME sound software on my system. Here is a list of what fails and what doesn't. (I'm sure there are other programs I could use to test with, but I don't know what they are since I am "just an average user" when it comes to multimedia software.)

These don't fail:

Amarok
KDE event notification

These do fail:

Firefox
Xine
Mplayer

In the things that fail it is only the sound portion of whatever (flash, mp4, etc) which goes away; the video portion plays normally.n I leave my system up for days at a time. The failure occurs some "long-ish" time (days) after I reboot. I have no idea what triggers it. I do not use sound most of the time, but when I do it's music through Amarok (which doesn't fail) so I do not notice the failure when it occurs.

It seems clear to me that it is NOT the failed programs which are at fault but it is, rather, some underlying set of sound libraries and/or servers used in common by all the programs which fail, and that the failure occurs when something happens which affects that set of sound libraries and/or servers. I don't think this is specifically a Slackware issue since I've seen a few other problem reports on the web where the sound simply stops on non-Slackware Linux systems. Some of the problem reports I've seen suggest that playing sound from one program stops sound from other programs. I've tried various combinations of sound-producing programs but none have triggered the problem.

I've looked at /var/log/{messages,debug,syslog} and see nothing relevant. I've gotten process lists from ps before and after the failure and no "relevant" processes have gone away. (But note, as before, that I am NOT a Linux "multimedia guy" so I can only make intelligent guess at what is "relevant".) Does anyone know what this problem is and, better still, how to solve it? Or where I could look for additional clues? Is there some way to "reset" the sound system without having to reboot?