Debian testing branch ((squeeze)) just went to KDE4.2
I decided to allow the upgrade and I had some sound problems.

When KDE4.2 was *not* running, sound was running great on a virtual terminal and in fluxbox.
When KDE4.2 was running... no sound... anywhere.
Hence, the problem was not with the soundcard or the kernel config, but with KDE4.2
It seems that knotify4 was not letting anything else use the sound card.

Well, if I kill knotify4 and restart it, then I have sound and everything is happy and joyful with sound. So, I added a quick and dirty kludge to ~/.kde/Autostart to kill and restart knotify4. Well, this is a crappy way of fixing the problem.

Does anyone have any further insight into the knotify4 problem, and a more elegant way to resolve it?

As usual, I managed to solve the problem within a short period after asking for help.

Here's the deal:

I upgraded from KDE 3.5, and in the upgrade, some KDE 3.5 packages were still hanging around.

I uninstalled all the leftover KDE 3.5 packages, including ARTS and kde-core

I also installed the KDE 4 "Phonon-backend-xine" and "python-qt4-phonon" packages.

Now, this fixed the problem in a non-barbarian manner, although I don't know for certain which of the above solved the problem. But now I have sound working in KDE 4.2 and everything is happy, swell, and groovy.