Hi rage,

Along with the other advice given, check your "Small/Large" speaker settings to make certain the back surrounds are set to "Small", no matter which processing mode you're using.

If the back surrounds were inadvertently set to "Large" in the THX mode, deep bass might overload the drivers at very loud playback levels or drive the Onkyo's surround-channel amps into distortion.

Regards,
Alan

Alan Lofft,
Axiom Resident Expert (Retired)