Thanks for all the feedback. The Paradigm Phantoms, which would be the mains, are a moderately-sized, floorstanding speaker, weighing about 33 pounds each, 37 in. tall, with a tweeter and two 6.5 in. bass/midrange drivers in each. They are part of a budget series a step below Paradim's Monitor Series. The seating area and speakers would be fairly close to the side wall, within about six feet of the main speakers, and there would be 18 feet between the front and back walls, or about 16 feet between the front speakers and the back wall. Any informed guesses about how that might work are appreciated.