I tried both suggestions below. The suggestion about running the mains and now my center
large works to great effect in taming the bass in my 20x20 room. The other suggestion of using cascading crossovers didn’t help as using the receiver’s alone worked perfectly.
http://www.axiomaudio.com/sub_setup.html
For Axiom’s larger tower speakers--the M80ti’s, M60ti’s, and M50ti’s--depending on the particulars of room size, start by selecting the "Large" setting on your receiver for the left and right main speakers, and "Small" for the center and surround channels. With these settings, and the subwoofer set to "On," most receivers will route full-range sound, including deep bass, to the main left and right speakers, and bass below 80 Hz to the "Sub Out" jack on the rear panel of the receiver. (Some rooms may benefit from smoother bass by getting deep bass from three room locations--the sub plus the main left and right speakers--rather than a single subwoofer.) If running your left and right fronts on "Large" produces too much bass output, change the settings for the mains to "Small."
In most systems, at least at the beginning, set everything to Small and the subwoofer crossover frequency in the receiver to 80 Hz. Later on you can experiment with different settings if you want.)
Note: If a user wants to experiment and set the subwoofer's crossover at the same frequency as the receiver's crossover, better integration of the subwoofer may be achieved. Experiments at Axiom have shown that with the EP400/500/600 subs, it's advantageous to do so because of the brick-wall algorithms in the DSP circuits.
I’m not sure why people care so much about others deviating from “conventional wizdom” (read Dolby and THX) with their own systems or recommending experimentation to others. I did so at the suggestion of Alan Lofft based on his comments in “Featured Articles” here on the Axiom site. While the standard settings are probably a great starting point for most people there is no reason to stay with them if deviating works better for someone.
