Further to my previous post, I have been trying to get the functionality I need using a winamp output plugin, but the only winamp plugin I find that does what I need (add silence between tracks) is gen_paus.dll which is a "general" plugin, not an "output" plugin, and so I can't import it into musicbee.
It would be an enormous help to be able to use this plugin untill a new version of musicbee fixes the intermittent failing of the add silence option...