Hi rmcgirr83,
It's placement, placement, placement! And the ROOM! Even identical speakers will sound different using a pink-noise test signal unless they are placed side-by-side. (Even in that setup you may hear slight differences; that's how hugely influential the room is in altering the sound of a given speaker.) Try it with your M60ti's, then place them in the usual positions. It's a very interesting experiment.
The center channel speaker is, according to all my tests, even more susceptible to changes in tonal balance. See my article, "Fine-Tuning Center Channel Sound" in the Axiom newsletter Archives. You can get to it under Audio Tips and Tweaks. Try the site map (bottom of screen) if you can't find it.
Try different placement of your center. Keep in mind that pink noise is a rigorously critical test signal. Use your remote and play movie dialog, switching from "Stereo" to a 5.1-channel mode until the dialog sounds tonally matched. With experimentation, you can get it very close. I also use music with a vocalist switching back and forth as I try different locations for the center.
Remember that about 70% or more of the sound you hear from a single speaker is made up of groups of reflections from all the boundaries and objects in your room; only a small percentage is the direct sound radiated by the speaker. This is why the same speaker in slightly different locations will always sound different using pink noise, because each change in location invokes a different combination of direct and reflected sound. Our hearing is incredibly acute in the midrange (evolution. . .), so we can detect tiny differences in coloration using pink noise.
Once you have a good location for the center, adjust its level directly with a few movies. Some are poorly mixed, so you may have to tweak the center level occasionally, but if you are having to adjust all the time, your center location is flawed.
Regards,
