Another consideration is the room dimensions and their impact relative to speaker and seating placement. I apologize if straying too far from the original question, but just trying to help.
In my similarly-sized room, I found that measurements using an inexpensive Radio Shack sound meter and the signals from a test CD allowed me to easily plot out room response(i.e. peaks & dips at various frequencies). Changes in seating and speaker locations as small as 3-6in. made an audible difference. I thought that a larger room would allow for more bass at lowest frequencies, but in fact that wasn't the case. Some spots had pronounced bass dips as much as 10db. By moving seating I was able get smoother and flatter response. The caveat being to keep in mind Bobby's advice on speaker location. Cheers,
Spencer
