As long as it is hooked up/calibrated correctly this really is normal. The rear channels will not be as noticable as the surrounds. A lot depends on the material your watching. Try finding a movie that is done in 6.1, like some of the newer Star Wars movies, you should hear some action then....

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
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