This sounds like a problem that I had once, and that Steve straightened out for me. At least before the firmware upgrade, one had to be in a surround mode before entering the channel calibration set up, or the sub trim will do nothing. Also one needs to be in a 2-ch mode (stereo, upsample...) before entering the 2-ch sub offset part of the setup menu before changing it. Steve also suggested I turn my sub gain (volume) way down so I would not need to have a -12 dB sub level and so the 2-ch sub trim could be useful over its whole range.