As has been suggested already, having 3 of the 590's behind an AT screen would be the most ideal, and also give it a cleaner look since the LCR would be hidden. Along with the the speakers being placed behind the screen you can also place your subs behind there as well. Notice I said "subs"? That's because you would be better served running duals vs. a single sub to get a better overall experience thoughout the room at at pretty much every seating position. I would also suggest going with the 18" variant to get better low end extension. A couple of those can be had going the DIY route (if you're handy and have some power tools), or look into some ID brands like Rythmik, PSA, HSU, SVS, etc.. FWIW, you can definitely get more bang for your buck (all puns intended
) for a fraction of the cost of purchasing manufactured subs.
With that that said, here is what I'm seeing in your layout:
1.) Where the 24' wall stops at the lower end of the drawing, you should consider walling that off with an entry door to seal up your HT area. This way you could utilize the length of that space to put the screen on one end (top of drawing), and would also allow you to put a second row of seating if you so choose.
2.) On the opposite 16' wall (top of drawing) is where you could frame up for your AT screen.
3.) As for the the 12' x 15' opening on the right side, you could use that space to set up a snack/bar area, and even house your equipment rack. Also, this area could be curtained off during movie time.
I know this may be more than what you had considered doing (I'm just guessing here, because I have no idea what your planned budget is.), but again, from what I'm seeing on the drawing, this is the route that I would consider going to maximize the potential in that space.
Hope this helps,