Well, I'm gonna give you the standard cop out answer to your question. Experiment with placement to see what sounds best. I don't think the pitched ceiling will be a problem. You might be able to put the 60s a little closer to the back wall, might not. You might be able to move the 60s a little farther from the side walls (ie. closer together), might not. Sorry I'm not more help, but I just don't have the expertise to advise you.

Jack

"People generally quarrel because they cannot argue." - G. K. Chesterton