John,
I have the M60s and originally had them about 12 feet apart, toed in slightly, with the listening position about 10 or 11 feet back. In stereo (i.e., no center channel) there was a significant "hole-in-the-middle" effect resulting in a marginal sound stage. Per Alan, increasing the toe-in wasn't a good solution. I think you really need to be at least as far back from the speakers as they are apart from each other to get a good sound stage. A little farther back doesn't hurt. I'm sure others have had different experiences, so it's just my opinion. When I moved the speakers about 10 feet apart and the couch back to about 12 feet from the speakers the improvement was dramatic. Having the center channel on improved the situation, but in my opinion it was only masking a problem. I personally wouldn't recommend the M60s for your current situation. I don't beleive you will get the most out of a very good speaker.
