jpw, I recommend using this: http://noaudiophile.com/speakercalc/ It has helped me with several speakers in different rooms. You don't have to follow it verbatim, but it is useful sometimes even if you only use the rear-wall-to-speaker dimension or side-wall-to-speaker and then experiment with placement from there. You can at least ameliorate or level out some of the room nodes until you get more familiar with the sound of new speakers, and how you may want to EQ them.