Set mains to large. Tell receiver that sub is NOT connected. The LFE normally meant for the sub will now be routed to your mains, but with an extremely reduced signal (to protect both speakers and amp). Like 1/20th is what I read.
Since most speakers are not actually full range, just use common sense, turn it down if it starts sounding bad.
Make sure to find the best spots for all of your equipment, and then run the Audyssey. Use all of the available measuring spots, which for you is 6, all around the main viewing spots.
After running the Audyssey, write down all of the settings it gives you. You can always tweak things afterward for personal preference. It will definitely give you xover points for center speaker and surrounds, and perhaps for the mains. If it does so for the mains, you can always defeat that xover, but know that Audyssey does absolutely no calibration below what it finds the capable range of a speaker to be. (For instance, if it finds a Bose speaker to work only down to 250hz, it will only apply corrections above 250hz).
Good luck.