@hillbilly559 I agree with @ghdprentice here. There is something very wrong here. You don't have to do any of these extra stuff to balance left, center, and right speakers. Marantz should have three options for the center channel: phantom, normal, and full range. I would first use phantom option. This will allow the left and right speakers reproduce the center channel. Use the built-in test tone generator and see if you get same sound from left-center(phantom)-right channels. I suspect your receiver may not be decoding the center channel at correct level. If that step works, then take the center per-out and connect it to a separate amp and connect your center speaker to that. If that works, then your Marantz amp driving the center channel is the culprit.
I have use Yamaha receivers in 7 speakers + 2 subwoofer arrangement and never had this problem. There is something fundamentally wrong here.