I wonder if you'd be better off with the stand-mounted 121s rather than the larger mbls. That way, perhaps, you could more easily move them out into the room for serious listening and get the full benefit of their omni-directional presentation, to which I also am partial. I honestly think that you'll never get to hear what they are best at with them close to the side and rear walls. You should take pokey77's suggestion and call mbl, maybe they can make a recommendation for you.
And I agree with prof, while I would not call imaging with the mbls I've heard to be "pinpoint" (which I find to be unnatural, by the way), they do present a very natural placement of stable and three-dimensional images in a soundstage, certainly not diffuse.