Unless you have a very unusual processor, when you set the crossover to high pass the mains/center/surround, all frequencies below the the high pass should be low passed to the subwoofer in addition to the .1. Running a center channel full range (unless it is enormous, which your’s is not; even Mark Seaton high passes his Catalyst mains for HT use, and they are huge) is only going to limit its output and increase distortion. You are also going to have phasing issues running your speakers full range with subs overlapping.
Most likely what you have heard at the demo was the subwoofer level was set much higher than the mains, given a big boost even into the 100-120hz range. It is done all the time to make demos impressive. While not technically accurate, many (possibly most) home theater enthusiast run their sub(s) hot. I suggest playing with that and/or adding addition subs to get the sound, not running your center and mains full range and over driving them. You may want to pop over to AVS Forums and open a discussion there, as they are home theater focused.
