The difference in sound quality between a poor sub set up and a great set up is astounding.+1
Earlier this year I added a REL S/5 to my system. Just a foot of placement and an inch or two of fine tuning was the difference between extreme room nodes and virtually no room nodes. The direction the cone points is critical. Distance from wall is critical. So is cutoff and volume. Now bass is tight and right, quick and integration is perfect, the sub is an inert box. I have full range speakers and irregular room dimensions, so that may have helped.