I can't get the danged thing to work on a model of mine either.  It is asemi--complex model.  It is a shrimp boat I modeled in B5..  I contains terrains, primatives, and several booleaned components.  When I put the model in B6, highlight (select) the entire model) then "collapse"  it, the export object menu can now be acessed.  All seems to be well until I then do a test import of the model.  The only thing actually saved was the boleaned wheel house.  the hull (terrains) masts, nets, etc... are not there.

Am I reading this correctly when you say each component of the entire model must have a negative something buried and grouped within it?  If this is true, merge is a better method.