I love your photo of the room, but to me those speakers seem to be in tight already without adding any more.
I've got a 5.2.4 Atmos setup and have it wired for 7.2.4 in my 240"L x 197" W x 96" High "games room". (~ 2625 cubic feet). I haven't enabled the 7.2.4 as I'm doubting the added benefit of the Rear Speakers. I do have the extra amp (my Denon AVR "only" has 9 channels of amplification), so it's probably only a matter of time before I cave into my curiosity.
Just a comment about AVRs, Pre Pros, etc., and heating. Back in Tech School, it was drummed into us that heat is a nemesis for electrical and electronic components. The rule of thumb was the hotter they run the less remaining life they have. (This is also true of electric motor and generator insulation by the way, as well as VFDs, TVs, etc. Another, even more pertinent rule was "never let the smoke out"
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Typically IEEE specs allow for a 40°C Rise of an ambient of 20°C. Above that degradation occurs. That's 140° F. At that temperature design life should be achieved. For every 10°C above the allowable 60°C it half life's the device. Now these are "rules of thumb" and not absolutes, but they guide me with every installation of electrical and electronic gear I work on. I have an infrared thermometer that I use to measure anything I think is getting close to warm. Even though my Denon AVR didn't get close to 60°C, I still put a couple USB powered cooling fans on it.