Thanks everyone.

I moved the sub for my home theater to the big room to try it out. It improved the sound considerably although still not as good as having just the M60s in a small room. Since I was hearing plenty of bass using the sub, I came to the conclusion that the room size/shape is simply not conducive to very good sound. However, I will get a matching sub like EP175/350 for my M60s. Thanks again for your feedback.