At the moment your front speakers are set to Full Band (Large) and your sub is set to LFE. In that setting combination you're only going to get bass content for any speakers that are set to Small and when there's LFE content in the signal. That might not be enough for you to get a sense that the sub is working. Try either setting the front L&R speakers to Small, or set the sub mode to LFE + Main.
Also, the sub shouldn't be booming out and rattling your teeth all the time. It should blend seamlessly with the rest of the speakers. When you switch the sub off and playback there's should be a bit of a hole where the sub was contributing (subject to settings), but it should always be in proportion to the sound from all the other speakers rather than sticking out like a sore thumb.