The problem is described here, and I found a solution (modified) here.
sudo apt-get --no-install-recommends install quodlibet quodlibet-pluginsThis installs Quod Libet without the unnecessary recommended dependencies.
The panel icon for Quod Libet is black and does not work well with the dark panel in Cruncbang. I have replaced the icon with one developed for the Faenza theme by ~poupoul2.
The notification icon uses the .svg icon supplied, but the panel needs an .png icon. I created my own.
Update: Icons can also go in the active icon theme. For me, the Panel > 22 folder.