Control: tag -1 + help The only requirement is that *some* GStreamer audiosink is installed, in order for Quod Libet to send audio to it. Depending on gstreamer1.0-pulseaudio doesn't seem reasonable since it would force pulseaudio to be pulled in even on systems that are not using it (and then still wouldn't work if the sink for whatever audio system you *are* using wasn't installed).
I'm not really sure what the correct way to get the right audiosink package installed is; anyone have an idea? I feel like this is the responsibility of the desktop task that you install, rather than something that should be solved by individual application packages.