I can't get x11amp running in gnome. It just scrolls through my song playlist really fast. I had this problem before installing 6.0, but I was able to get songs playing by starting another random program(normally a terminal) right before hitting the play button. I'm not sure why, but this seemed to free up the sound device for a split second. Now, not even this will work. There seems to be a conflict between gnome and /dev/dsp. If I try to "play" the sample.au file that comes with sndconfig from the terminal, I get a message saying that /dev/dsp is busy. In addition, it does not seem to matter if sounds are enabled or disabled in gnome and enlightenment.
probably esd is running. Try editing the preferences in x11amp and changing the output plugin to the one for 'Esound Daemon'. Does that help?