convert that to editable poly like all the other meshes are.
attach all the other meshes to the box.
select the box via "element mode"
delete box.
done deal.
you might need to re-arrange the pivot to the center of the object. to do this, click on the "hierarchy" button (third button, next to the one called the "modify" (which allows you select the element/poly/edge/vert etc), with the model selected, just click on "move pivot only", and then click on "center to object". once you do that, click on the "move pivot only" to deselect it, and then go about your business modelling etc.