Place the speakers back-to-back. You'll have a bipole sound radiation pattern with sound emanating from the front and back and diminished levels to the side. Mirage has made a number of great sounding speakers along this design principle. You'll need to position the speakers so that there's plenty of space to the rear wall (3 feet minimum, but the more the better). You should get a big, spacious soundstage with large-scale dynamics. All the setups will result in noticeable phase inteference problems.
