First time home theater owner (please help).

[Steelmaker]

I have a question. I'm running an Onkyo 606 with Polk Audio RM 6880 speakers in a 5.1 setup. Everything sounds good except that the rear speakers are not as "robust" as I had thought they would be. I've tried all kinds of blu rays with different audio standards and yet I come to the same conclusion everytime. The overall enveloping sound is good. It has great clarity and booming bass. However I really thought I would be able to hear more distincitve sound effects coming from the rear speakers. Sadly this doesn't seem to be the case in most movies. Infact I'm a bit surprised at the lack of rear speaker use in just about every movie I've tried. Even the lossless audio tracks. I thought I would be constantly hearing effects coming at me from the rear speakers. This is my first surround sound system so maybe my expectations were a little high. However there's a setting somewhere that I cannot help but think I am overlooking. Can anyone provide me with any suggestions on how to improve rear speaker performance?

All the settings seem to be correct. I did the auto calibration with the microphone and I have all of the correct PS3 settings based on the suggestions here in the forum. The receiver is set to "multi-channel" and I always make sure my PS3 is playing in "Linear PCM."

Before anyone makes any suggestions, let me first describe my equipment and setup.

Player: PS3 60 gb
TV: Sony SXRD KDS60a2000
Receiver: Onkyo 606
Speakers/Subwoofer: Polk Audio RM6880
Theater Room: Rectangular at 9' x 16' with the TV and speakers
against the wall, centered and running parallel with the length of
the room.
Connection: HDMI from receiver to TV and from PS3 to reciever.
16 gauge speaker wire.
Viewing Distance: 8' 3" with the rear speakers mounted in the rear
corners approximately 2 feet higher than the listener and facing slightly
outward from the listener.

Also, I noticed that under the audio settings I can adjust the decibel level of the front and center speakers and the sub woofer. However there doesn't seem to be a decibel setting for the rear speakers. Can someone tell me if there is such a way to adjust the decibel level of the rear speakers? This may be my problem even though it's at the settings that "Audissey" put it at.