Niv, it's unfortunate that there appears to be a defect in the circuitry of your EP500, but Axiom will continue to work with you to correct it.

As to the amount of sound from the back surrounds, yes very little 7.1 material with discrete back surround content is available, but when using DPLIIx mode all 2-channel and 5.1 channel material sends sound to the back speakers. This may be relatively subtle, but switching the back surrounds off demonstrates that there is a difference.

Enjoy the music, not the equipment.