The freedesktop new IM sound is just too quiet. Change to the bell
instead.
# (x=attention y=muc unread buffers z=muc unread buffers with attention sign)
#
# Sounds from the freedesktop project (available by default in Xubuntu)
-CMD_MSG_IN="/usr/bin/play /usr/share/sounds/freedesktop/stereo/message-new-instant.oga"
+CMD_MSG_IN="/usr/bin/play /usr/share/sounds/freedesktop/stereo/bell.oga"
CMD_STATUS_ONLINE="/usr/bin/play /usr/share/sounds/freedesktop/stereo/service-login.oga"
CMD_STATUS_OFFLINE="/usr/bin/play /usr/share/sounds/freedesktop/stereo/service-logout.oga"