OK. I'm not even supposed to me online right now (doctor's orders as I am supposed to be prepping for a sleep study), so just a couple of quick thoughts that I am more than happen to expand on later.
Direct firing is ideal for all speakers in an Atmos setup. This does not mean that you can't have good success with some awesome QS speakers, but you need to be able to "plot points in space" which means having straight firing sound from every speaker in order to plot those different points. Diffused sound from quadpole speakers is not good for this. Even bi/di pole aren't great, but some have their uses with multiple rows of seats, but still direct firing is how the system was designed for home use.
Speaking of seats, where are they going in the room? Based off of your Atmos overhead speaker placement in the diagram that you linked, you are sitting smack dab in the middle of the room. Audio likes things in thirds. I would move your seating so that it is about 1/3 from the back wall, or obviously, 2/3 from the front. Adjust your overheads to form that Atmos "box" evenly around your seating area, and then push your side surrounds back a little as well.
When pushing those side surrounds back, don't be afraid to having them slightly in front of the seating area. For me, I have mine about lined up with the middle (from front to back) of my reclining seats. So about even with my head when sitting up. We ALWAYS recline, so when reclining, they are now just slightly in front of the listening area. Works a lot better than when they were in a traditional surround placement just behind the listening area.
Also, put your side and rear surrounds down to just barely above your ears, or as low as you can go without them being blocked by seat backs, or heads from people sitting next to you. This will give you more separation between the surround speakers on the walls and the elevated overheads.
Lastly, be cautious about corner loading your subwoofers. You will "excite" more of the modes of the room, but you will get more "boomy" bass. I know that you are limited by a fireplace, windows, doors, etc, but having one up front in the middle (right where the fireplace is at) and one in the middle of the rear wall is best, or one in the midddle of each side wall. Again, I know that this won't work, but I just want to mention it. For me, I ended up with my 2 large subs up front, originally about 1/3 from the left and the right walls, and then I did some room tuning and tweaked their actually locations literally by inches until I got the response I wanted. So maybe under the windows (as long as they don't rattle). If they have to be in 2 corners, maybe look at the front 2 corners, and try to sneak them away from the walls/corner as much as you can get away with.
Alrighty, time to go to sleep before I get in trouble. LOL.
