Help - How important is the center channel Amp?

I would say that untill you replace the rear channel speakers to voice match the fronts, I would go with a good 3 channel amp. Most of any shortcomings between the fronts and center you should be able to adjust them out with your pre/pro. You don't mention what amps you are using?

How many people for the theater? If it's one or two, I would recommend you do a phantom center and spend more money on the 2 channel amp. My personal reference system is using phantom center and I own the expensive well matched center and amplification, so it's not a cost issue. The quality of the sound is simply better in this scenario with the phantom center. This can only work though if your viewers/listeners are relatively centered between the main speakers. If they are off center too much it heavily degrades the localization of the dialog, and is not advised.

I plan on using the new Ayre monoblocks and either a Meridian 2 or 5 channel amp (I also plan on getting the Meridian G68 as the pre/pro).
Why is it important to voice match the rear channels? Not to be cute but there aren't many voices coming out of them. ie. isn't it mostly sound effects and background?
Also, importantly, the center amp issue seems to me to be an issue of quality not quantity (am I wrong here?) so I am not sure how the pre/pro can adjust for that?

I had given serious thought to not getting a center channel since most of the time there will be just one or two people. Now I am leaning towards getting one. Most music people seem to think its not necessary, but most HT people I have talked to say yes. And while not a primary concern, it does seem a little silly to have spent all this money but not enough if I want to show off my system, including a new TV, to a larger group of friends.