If i were you i would first check the volume of center channel in the receiver settings and increase it. As such, most people i know keep their center volume 2 or 3db higher than other speakers.
If you are still not happy, then you could change your center channel. My personal opinion is that timbre matching the center with L and R is a little overrated. I have noticed that about 60% of the movie sound comes from center channel and there are very few scenes where sound pans from left to center to right. I feel i will not mind that, so i don't think i will necessarily want to have the speaker from same manufacturer for the center and L/R.
I myself am considering changing my center channel. I have a treated, dedicated room and want a beefier center channel though my current one is pretty good. I am considering one of the following - Polk tsx 250c, Focal chorus cc700 or Klipsch RC 62ii.
One thing that you will have to watch out is the sensitivity of the center channel. Because your receiver may not have high output power, you will need to get a speaker that has a sensitivity of 90 and above. Hope this helps