Samuel, I suspect the fact you haven't done anything with the level of the center (and, I suspect, any of the other speakers) has something to do with the problem. I'll let Wayne continue with suggestions. He's more patient than me.
Well, first I would say a big part of your timbre matching problem is having the center speaker largely hidden behind the TV. It is not usually possible to have vertical alignment of the center speaker, so it is usually either directly above or below the screen. I prefer it above, but others...