Stay with me here. It's a one step at a time process of elimination. Set the crossover to 80Hz and leave it at about 40% power. Also, be sure that the sub is set to LFE (or Normal) in the sub setup menu. It's a 150 watt sub that is spec'd to go down to 24 Hz and max output 115 dB. At these settings you should be able to hear the bass just fine. Since you can't, it's on to the next step.
You should have a setting that allows you to adjust your left, center, right, surround and sub levels relative to each other. Where is that set?
With the settings as above, raise just the subwoofer level in the channel adjustment section. What happens?