Rick is correct, that the middle of the room is usually a null area. 1/3 or 2/3 back may be better. Is your sub up front?
From reading your levels to me it sounds like you have it turned up fairly high (9 o'clock is loud for the 500). I run mine between 6 and 7 o'clock, receiver at -7dB (other channels near 0.
Did you calibrate with an SPL meter? The other sub setting not mentioned so far is the phase. Make sure it is not fighting your mains. The easiest way to get this right is play the receiver sub test tone (which is crossed in with the mains if they are set to small) and choose the phase setting that gives you the loudest SPL reading on the meter.
I feel the crossover of 80Hz is ideal for movies with a good sub and setup. 60Hz may be fine for M60s or M80s, but not for QS8s or the VP centers.
Your sub is working right, I mean you should be able to hear it easily when playing test tones or music???
Good luck.
