I have found that the delay setting helped my effects. Boost the rears to 6db+, set the correct delay for the rears...dont get the bar too close to anything (sides)...
You should be golden.
I sometimes get so obsessed with tweaking stuff on the bar and the AVR, that I forget to watch the movie. The girlfriend gets so mad when I pause it every 5 seconds to change something!
I added two speakers in the back and I am impressed with how wide the soundfield is. My room is terrible acoustically, but it really jams with my setup.