Tater, your 4' distance from the back wall can be considered marginal for getting benefits from back surround speakers(I often say at least 4' is okay, but this isn't something that can stated with precision). The scarcity of material with discrete 7-channel content isn't necessarily a decisive factor. Modes such as DPLIIx expand ambient content in two channel material(present in varying amounts)in to different signals to left and right back surrounds(one center back surround doesn't do the same thing)and also expand the discrete side surround material in 5.1 material to the back surrounds(leaving the front channels untouched, since there's already surround material in the side channels).
If back surrounds are used in a 7.1 setup the side surrounds are best placed directly to the side of the listening position, to give the best side effect(not extremely critical, especially with QSs). If there're no actual back surround speakers used, the side surrounds might be better placed a couple feet farther back to lend a bit of a phantom back surround effect.
