Center and Mains

You can change the speakers to match. Here is the matching center for your L&R that is recommended by Def-Tech,

http://www.definitivetech.com/products/cs-8080hd

An amplifier will do nothing to overcome the timbre mismatch.

In a 2 channel system, the speakers create a balanced image with sounds that come from anywhere in between the 2 speakers and even outside the speakers. Now if the 2 speakers were different, that image would be totally ruined.

In a multi-channel system, that perfect front image can be created with 3 identical speakers, however that is only possible in certain situations. The next best option is to use the timbre matched center that was designed by the company to go with the L&R. If seating is tightly centered between the L&R, the "phantom center" that was mentioned can work well in some cases. Any other center speakers will just degrade the front sound, and IMHO, trying anything with amps, processors, etc is a waste of time. Doing this will always make it sound different, but never right, and your ears know that. When it's right, your ears won't tell you to "clean up" the sound.

Lol thank you. Good points. I had auditioned the 8080HD and frankly (it could have been me), but it didn't even come close to making the grade. To me it sounded "thin and without body". I wish that wasn't the case, it would have saved me about $6K. Nevertheless my investment has been made so I'll look forward to Bi / Tri-Amp testing!
Thanks so much guys for offering up your experience and ideas.

Mac's are not known for having great speakers.  You really should consider a new center.  USAM has multiple pairs of Def Tech speakers listed that will match the sound of yours.  You don't even need a powered sub in the center so something like a 450 might work for not much money.  Buy a pair and only use 1. Or, if you want to go crazy, there is a pair of 7004's listed...

Otherwise I totally agree with comments above about going "phantom" for the center.

My question is can I add power and find those nuggets or should I
forget the power and find the right processor?

The processor it is. MX122, Marantz 8802A?? 

You have received a lot of great suggestions, almost all of which was to try and match all your front speakers first but it sounds like you want to get a new processor any way. So, let me make this suggestion. Buy a used processor first, maybe an MX121 or an 8802, see if they make the change you are looking for. If not, since it's already depreciated, you can resell it and not take too much of a hit and answer you own question as to whether a different processor will do what you are looking for. I think you will take the greatest "hit" on trying to re-sell a brand new processor as far as equipment goes. They just seem to drop like rocks pretty fast. Just my $.02, good luck either way!