If by the shelf you mean the one almost at the ceiling, I think it's a big trade off.... I mean, you have to weigh sound quality versus aesthetics and which you weigh more. S-150s off axis response is good, but, that high is asking a lot. The question is really how much you care about the sound versus the room aesthetics. Or how much the wife will let you get away with.
And those are all reasonable things to address.
If you can wall mount the S-150s ear level for the L and R, and wall mount the center pointed down at the listening position thats probably the ideal situation that is still relatively piratical.
If you could wall mount the left in that recessed area it would get it away from the wall a bit and clear up floor space. Granted it still sticks out. The Center I'd probably mount right above the TV pointed down, the right I'd side bracket mount as well.
Using the door as a reference, I'm still having a hard time seeing how an 80" would fit on that wall with any reasonable symmetry for placing the speakers.
I admit to being a little stuck for suggestions. I've even considered the wall that adjoins the guest room since that's clean and you could drop wires down that wall...but then you couldn't see the TV from the kitchen and I'm not sure how important that is to you.
Ideal? Nix the fireplace and make the wall flat. Then you can wall mount the speakers on brackets and center the TV.