A couple of bits of information to help you. I am an industry professional with over tweenty years of experience.
1: Planners can not work in a room of this size unless they are gigantic and really expenisve.
2: You must control slap echo and other room anomolies but using acoustical control devices, RGP, Echo Buster, Skylines, Carpeting, underlaying ASC tube traps, etc.
3: The other possiblity is to make the room smaller and more acoustically managable by building a partion wall.
4: You can throw money at the problem and use speakers capable of filling up a large room and which generate prodigous bass response. Check out Escalante Designs Freemont: 93 db sensitive, handles 1,000 watts, bass down to 18hz these are marvelous speakers built by the famous designer Terry Budge, who was the man behind Wilson's most famous designs. These speakers are $15,000.00 but will easily compete with speakers costs much, much more!