My M22's are approx. 8-feet apart and they sound wonderful in 2-channel mode with me sitting around 10 to 13 feet away from them. They sound equally great even when I am only 6 feet away from them.
I did once place them just 6-feet apart but it was for a DVD movie that I was playing. Didn't notice any significant difference but frankly then I really wasn't listening very carefully.
You should look at some of the pictures in the Axiom Wall-o-Fame
to see how far apart users are actually putting their speakers.