Well, a default Etch install comes indeed without alsa (unless this changed).
All I had to do was pretty simple (I don't use KDE).
I first installed alsa-tools and alsa-oss with apt.
Next alsaconf configured nicely.
As you noticed, many apps aren't configured yet for alsa(xmms, mplayer, ...).
Changing this in the app(change the output to alsa) itself fixed all that.
Some software isn't yet alsa compatible (or gives you blurry sound), luckily alsa can emulate OSS for them.
To do this manually, run "modprobe snd_pcm_oss"
as root(this should also fix the flash sound problem).
Blurry sound in alsa(DOOM3 Quake4, ...); first make sure you loaded snd_pcm_oss, next start your game with "+set s_driver oss" (example:doom3-demo +set s_driver oss) and it will remember from now to use the oss emulation.
No sound in Wolfenstein ET; again, make sure snd_pcm_oss is loaded and next type:
echo "et.x86 0 0 direct" > /proc/asound/card0/pcm0p/oss
...and that's about it (or at least what I remember)
except for not being able to play sound in more then one program at a time
That's cause of KDE's sound deamon(artsd) and not really alsa related.