Well if you insist on going with a single rear channel verses two, you will not have discrete R/L sound in this channel. What you will hear will be matrixed sound from the R/L surround channels. In this case, the obvious choice is to go with a non directional speaker such as the QS series. I would not use a direct radiating speaker unless you run two for a 7 channels sound, and only if you have plenty of distance between the speakers and where you plop your ass down, 6 feet or so.
Whatever you do, you'll enjoy the rear channel and don't believe those who tell you differently.
