My room is exactly the same width as yours, 9 feet. I don't have nearly as much length though at 12 feet. My LRS's are 46inches off the back wall and 38 inches apart from edge to edge of speaker.
I think the LRS's are a perfect size for this room as I am having no issues with sound stage or imaging. They sound GREAT!
And is your McIntosh overkill for the LRS's?
From everything I have been told and have heard, the LRS's thrive on power. So the more quality watts, the merrier. And with your 312, those are quality watts. I am powering mine with 80 watts per channel right now and it is not enough. The amp I am buying for my Maggie's is rated at 450 watts per channel at 4ohms. More power equals happy Maggie's!
I think you will be quite pleased with them in your room. They absolutely need help on the low end though. The bass the LRS's have is musical, defined, articulate, fast but a little lean.
Get yourself one or two quality musical subs that move fast enough to keep up with the Maggie's speed. I have narrowed my two choices to either the REL T5i or Rythmik L12. X2 on both. Will load the subs in the corners of my room.
Here is a picture of my LRS's.