That’s a nice looking room!
Tough call, but I think that center would work pretty good. Seems like a done bun.
If you wanted to get really invasive, you could open the wall up a bit and cut off the stud as I really doubt there’s any structural issues that would come from doing that in that area. Then just mount the new one and done! Or..... open up the wall, cut off the stud and header it off above and below what would be the Sheetrock opening. That would still allow dog ear functionality and shore up the interior wall. However, I still think if that little section of 2x4 missing will compromise anything, you might wanna check other areas of the house(consult your builder, WINK
)
Also, you might think about a heat shield if the chimney ends up close to the back of the speaker.
Going above the tv will probably sound fine. I think as long as tweeters are between 12-18” of each other vertically speaking they’ll be ok.
Or just buy the slim center.....lol!