Hey Brian, I believe they were talking about a strictly stereo plus sub environment. I don't see where anyone said that adding a center would or would not change things for him. That would be a whole other discussion. A good discussion, but different.
I would also be curious to know what sub you are using and how hot it is running. My EP500 does blend nicely with my M60s but from the specs and what I have heard of M22s, I see no reason why it would not blend equally as well with those.
Now in contrast, I tried using an old Sony HTIB subwoofer that I had left over with a second set of M60s in another room. Even though it was less powerful, by the time you turned it up loud enough to make a difference in this large room with M60s, it sounded way too boomy. Although it could play loud enough for this very large space, it was far from musically satisfying and I removed it altogether.
I could see how a similar scenario might lead you to believe that there is a "gap" between the two. It may not be a gap. It may just be that you need to calibrate your sub to match or that it plays a bit more 'boomy' than the detailed M22s.
Geez, what version of the M60's do you have ?
I may have to take a trip over to the Island with my M22 and we can do some comparison's.