As long as you make sure that the front baffles of the speakers are "proud" of the shelves, etc, you shouldn't have any trouble with ported speakers there. You ARE going to get some potentially detrimental effects from having them in a "cabinet", but if that's your playing field, well, play it.
I was told by someone who I consider credible that the minimum rear clearance for a ported speaker is only about 1.5 times the port diameter.
You could also consider using VP100's in that space. They are sealed and oriented horizontally. No reason you couldn't use "center" speakers as mains if that is your "best" solution. It doesn't sound like you have room to stand a M22 in there anyway.
I'd post a couple pictures and call Axiom.
