While you're playing with positioning the side surround speakers, I have a suggestion. In addition to Larry's recommendation to place the direct radiators beside your listening position, also try placing them slightly to the rear. Assume a compass circle around your listening position. Directly to your right would be 90 degrees and left is 270 degrees. Try moving the right surround back to about 105-120 degrees or so, and the left to match. (Mine are at 108 degrees, which several sources cited as a good location during 5.1 days). Then, play with the angles from those points (I have mine pointed forward and down, to fire directly at the listening area, after a suggestion from Matt). Just an idea, but I really like the sound. It helps to slightly mitigate the "pronounced stereo separation" that Larry mentions.
Reference two center rears: I used to do the same "PL decoder in the back" method that Larry does. If your PL amp has outputs for two center speakers, you just plug one speaker into each. The way I did it (I seem to recall from one of Larry's posts that he does the same) was to run a Y splitter from the center out jack on the PL amp to another stereo amp and plug the two center speakers into the stereo box.
