VLC may not depend on the desktop environment in order to play audio files, whereas amarok and other apps do depend on KDE configuration in order to work. So, investigate KDE configuration. In Yast, (Kmenu - System - Administrator Settings), click on Hardware, then click on Sound to see if KDE recognizes your sound card.
Also, if you have hwinfo installed, in a terminal, try 'hwinfo --sound'. What is the output?
You could also try playing an audio file from the command line. What error messages do you get, if any?