First, I'd verify that the distance settings for all speakers are reasonably close to what my tape measure tells me. Second, I'd run the manual test tones while sitting in the first row to get a feel for how things are balanced. At that point, you can also experiment a bit with running the surrounds a bit "hot" (maybe a couple dB higher than the meter and auto-calibration suggest) to see how that works for you.

Another thought is to start out with some well-selected test material. Some offerings simply don't give the surrounds much to do, which can leave you a bit disappointed. Try some good action DVD's (I'm sure we can get some suggestions from the crowd around here, but a few ideas that come to mind are Gladiator, Attack of the Clones, U-571, The Incredibles, Lord of the Rings, ...) and see if the source material has been contributing to the sense of "weak" rear channels.