The basement room I plan to put them in used to be a garage, its 17 by 26 (long and narrow). The ceiling is about 7' 8" and has a beam running crosswise that comes down another 10". Im concerned that if I put the speakers in front of the beam then the sound will be markedly different behind it (or vice versa).

I know in real theaters they use multiple sets of direct radiating speakers along the side walls.