I checked this out the other day. The center speaker does indeed play music, but how much is very subjective. I think, mainly, it is used for the sync voice and navigation playback (though I could be mistaken). I'm leaving mine stock. It is such a minor addition to the sound (at full volume I didn't even know it was working until I put my hand on it, and even then I wasn't entirely sure at first if it was sound or just vibration from the rest of the speakers.) Though, since it is playing music (and I'm not sure if it is a separate signal from the factory processor or not), I'm going to be sure to run it through my summing device, just to make sure I'm working with a fully re-integrated signal out to my amps.
Either way good luck with the upgrade. I'd love to hear your take on it after replacing it.