I say get the center that fits and enjoy it. Are in-ceilings the best...nope but what you have here is 1,000x better than just using your TV speakers. I use in-celings for my surrounds and they are fine. I use them in a 2 channel set up in my bedroom and they are great for background music.
Timber matching is more important if you are listening to multi-channel music, for TV and movies you will be just fine.
The sub is fine in the rear. Mine actually works best there(less standing waves) even though I have it in the front now.
Now, the most important thing that you can do is get off here and never look at this forum again. I popped on here to "show off" my little system many years ago and now, several years later, I am missing $30,000 if not a lot more.
The system that started it all:
Things got crazy for awhile:
Even spread into the office:
And the bedroom:
And outside:
I finally got over it and just have a basic TV set up in the bedroom, nothing in the office and I sold one sub. This leaves me with a good place for movies and music and now my wife doesn't think I'm crazy.(other than my bike obsession)