Grador is right on with the phase switch, however I wouldn't necessarily just crank the sub level all the way up. IMO, controlling the sub through your denon will get you only so far. I like being able to make more precise adjustments using the subwoofers knobs. I usually set the sub to about halfway, calibrate using the receivers onboard system (audessy or something else) and then go through and then tweak the settings to taste. For certain content using the knob on the back of the sub provides me with more useful fine adjustments as I change content.
You didn't say, but I just want to make sure you have all your speakers set to small and the crossover set as high as it'll go (120 hz I think). Your satellites and center are both rated something like 115hz and 110hz on the low end, so you need to make sure your crossover setting is set correctly.
Other than that it's all placement. Finding the best place for the subwoofer can be a pain in the butt. The crudest method involves a lot of crawling, but can give you amazing results, depending on how far off you were in the first place. If your main use is HT I would seriously consider a second subwoofer as well since getting even coverage with only one is nearly impossible without something huge and expensive.
