did you calibrate the spl levels of each channel?
I'm fairly positive it's not the receiver. I think it's software related, I just can't figure out which options to tweak.
do you have a digital out from computer to receiver?
I have a feeling you have actually disabled the other channels as opposed to down-mixing to two channels. So you are just hearing what is supposed to come from left and right and missing all the sound from centre.
