Hmm...well I wish I had better advice. I typically run GNOME / fluxbox.
See if XMMS will work with ARTS as it's output plugin. If that works then you know it's ARTS. If it doesn't work with ARTS but works with ESD/OSS then you know it's ARTS you have a problem with and you can try finding information on that.
P.S. You might want to try the KDE board too @ http://www.kde-forum.org/index.php