Assuming you haven't acquired them already and are itching to install them, you would probably do better to take a close look at your current speaker placement. You have plenty of speaker for your space.
Our rooms are close to the same dimensions, so 5.1 should be very enveloping and effortless in yours. Mine is 12' x 17'
First I will say that optimising your mains for stereo listening will create an immersive experience alone.
So I recommend staring there.
Before doing any adjustments turn room eq off (audyssey, Mcacc, ypao etc.) Axiom speakers are relatively flat, so with proper placement you may not need "help" from an eq.
First move your front mains 2' off of your front wall if you can. The center channel will also benefit from getting off the wall. This should improve any bass null and cancelation issues-- while moving the soundstage forward.
Next look at speaker toe in and distance from your listening position. For my setup, the mains are approx 90" apart and my seating position is 13' off of the front wall. Experiment with messing with the toe in angle-- makes a huge differnce. Even a couple of degrees one way or the other will often make appreciable differences. Grab a cheap line lazer or pointer to align the speakers with your seat and track adjustents closely and listen. A string taped to the back of the speaker and stretched out also works.
Use a good stereo mixed CD to make adjustments. I used Mumford and Sons sigh no more for mine. The main vocals should be centered even though the center is off. It will give the illusion of a single singer surrounded by the band. Now that that is set, level your speakers using a bubble level on top (level sideways and front/back.) It makes a big difference with detail and transparency when your speakers are properly aligned with your ears and eachother. The rest falls into place-- as center channel and surrounds are easier to place.
You should get leaps and bounds better if you are out of whack.
Hope this helps. Why am I always so long winded?.....