The guide is to have one release with everything and a medium for each cd.
See the following thread for discussion on what to do with this sort of thing.
2-in-1 release groups and other boxsets (STYLE-330, STYLE-331, STYLE-335):
See http://musicbrainz.org/series/b43b4a74-52d5-4d79-98d9-be3188176a68 for examples of this sort of thing.