Well, even at 13' from the center of the couch, it's only a small move forward from the current position, and doesn't pose much of an issue. It may help the sound imaging slightly since the distance between the fronts cannot be further than 7' apart. The theater room I helped build for my parents wasn't much wider (I think 10' or so) but it was a long room with stadium seating, so distance from their 100" screen wasn't much of an issue either, lol. The sound imaging in their 7.1 setup is great, but again, the room is much narrower than mine, and has drywall/carpet and no windows.
I guess the real answer I'm looking for (other than layout tweaks) is how much will it affect the power to the front 3 speakers having to run a 50' wire to them? I'm not too savvy on the loss of power, say from a 120-130watt per channel signal. I realize that power isn't driven constantly, but I always like the clean look of not having a half-dozen source units lit up in a tv console below the screen. I suppose I could put the AVR up front and run a few HDMI lines to the closet in the rear of the room in order to feed the signal from a BDP, HTPC, etc. Any thoughts on that option?