I decided to play around with the crossover frequency between my sub and the main left and right speakers today. It seemed to make a little bit more of a difference this time around. I think I may have messed something up in the process last time. The biggest changes occurred in the region from 90-100Hz. 40Hz seemed to flatten out that area the most, but also led to a little less output in the lower range and a sharper drop at about 115Hz. It looks like 60Hz is the happy medium in this case, so that's where I'll keep it for now.