I have a friend with a very similar Klipsch system...very much into his system. He has a Klipsch sub that he thinks is killing it (has it turned up to near max). I've told him twice if he wanted to take his system to the next level he would upgrade the subs.
They make a bigger difference than you might imagine.
My system
View attachment 33866
IMO...it's great you have ceiling access to install inceiling atmos...if I didn't mentioned...6" speakers work, especially for 8' ceiling...8" speakers have wider dispersion...you don't need to break the bank on these...I used mid level Polks $300/4.
Front
View attachment 33871View attachment 33872
Rear
Side surrounds...you mentioned something about those not being optimal due to the layout. Just a note, the side surrounds make the 5 channels, you get more content going to those speakers than the rear surrounds
Good you've learned something here, I know I have....good luck with the project. Keep us posted.