That's the right connection on the receiver (SW preout) and the settings seem okay on the sub. I own this sub model and it does put out good bass. The volume doesn't need to be up that high on the sub under normal circumstances, but I understand why you did it here. You might be turning it back down if you find out what is wrong. Might try the sub's phase setting at 180 just to see if it improves things, but if it doesn't, switch it back to zero.
There are additional subwoofer settings in the setup menu on the receiver as well, and it could be turned way down there. Could also be the receiver's sub out crossover (try it at 80hz.)
Did you use any room correction programs in the receiver, like Audyssey?
Don't believe everything on the Interwebz! A duck's quack DOES echo!