It pains me a little to say this OP, you seem like a swell guy, you earnestly want good audio, you're willing to spend some to get there:
But if it was my place, and that's the only place the TV could go, right above the fireplace, with only that little space around it, somewhat shoved in a corner . . .
I'd just forget the audio hunt entirely, and use the TV speakers. I might split some hairs, ask around, to see which of the TV candidates might have more acceptable sound.
For the hassle, the detraction from the looks, the compromise of setup, that is just my honest statement, and that comes from someone who has a bunch of speakers right now.
FWIW, I've suggested a similar thing to at least one good friend of mine, and I'm pretty sure to my brother as well for one particular setup he was thinking about.
Maybe I'll change my mind if something dawns on me, maybe I'm missing certain possibilities.
Lastly, I would never run the fireplace at the same as the TV, and I probably wouldn't run the TV for quite a while if a fire was recently lit up. But then again, mine would be a huge plasma.