When I kept discus I kept them with angels and they did well enough together. The diesease rumour (angels and discus share dieseases, angels resistant, discus not) is pretty well unproven. Gouramis I never kept much, but I also kept discus with a variety of plecs, cories, dwarf cichlids, small cichlids like Biotodoma, and I found them very similar in character to angels. I think most people have horribly nercous discus as they keep them in bae bottom tanks with no other fish in too small numbers.