There have been many discussions on this site (and others) regarding the timbre matching of the front three speakers. I searched "timbre match" and came up with about 34 threads where this has been discussed. Basically, you want all three of the front speakers (L,C,R) to be matched acoustically. This is so that when the panning of a sound, a car / airplane / etc., travels from one side of your room to the other the sounds flow evenly from speaker to speaker. Usually timbre matching the front 3 speakers means that they should at least come from the same manufacturer.
I would say that if you absolutely cannot place the center anywhere else (possibly on a bracket extending from the wall), then you should look for a center speaker that meets your needs and then get the fronts that match that particular center.
