RPG omnifussor and hemiffusor are good choices. However I have reservations about BAD panels for first reflection points. They seem to have a rather stong specular reflection. I'd readily use BAD panels or VariScreen in other areas for bass absorption and generalized diffusion. If you could afford more absorption, I'd consider RPG's Abffussor for first reflection points on the side walls and back wall. Alternatively if you have adequate distance from the rear wall to listening seat, diffractals would rock! I suppose rigid fiberglass would suffice for many surfaces but RPG's diffsorbers have a special allure of efficiency and versatility in small rooms. Too bad they cost an arm and a leg.
Tumara Baap