Hi Jeff,
Alan Lofft posted this guide on speaker placement which should help you find the right location for your speakers.
http://www.axiomaudio.com/archives/home_theater_layout.html
I have the same speaker set as you except my subwoofer is different. My room size is 20 feet wide by 14 feet deep.
My guess is your front speakers will be no more than 15 feet apart but probably wider than 8 feet. You might want to adjust them depending on your personal likes for sound stage and how closely the sounds match the on-screen action. I found the ideal relationship to the on-screen action occurs when the speakers are spaced just outside the screen. However, I have mine wider than that as a compromise because my screen is much smaller than yours and I wanted a larger soundstage for music.
Your rear surrounds will probably be around 10-15 feet apart based on the information you gave on the Seating position. (based on the recommended range of angles)
Not exactly sure how your side surrounds will deal with that post in your room. I sounds like it might be in the way of your side surround speakers, but perhaps locating them just behind your seating row will get the post out of the way.
Have fun. You're going to love those Axiom speakers.
