Actually, I have to take that back. Some of these systems are older and I need to take a look at them because I haven't in a while as I work on new things. The abstraction in the XML makes it a 2 step process, but the XML also has things that the files don't have. For things like Halos (which are just bitmaps) there's their general sizing and distance data, and for things like sounds, there's the general distance/loudness settings.
So, basically, for everything but music, once you drop in a file (like a sound, crosshair, halo, etc) you'll need to go into editor, into setup -> right section and then add it, and hook it up to the file.