I really love the red room light and curious to know how you achieve it. Because it’s getting closer to Christmas maybe you should enhance the room with some green lighting too . My thought is to introduce a few pieces of furniture into the room to get rid of the open space and you have a lot of acoustical stuff going on in the room especially in the rear wall. I think furniture spread throughout the room is the best diffuser in the world. I've always wondered what a few diffuser panels on the wall really really do, most of the time it's a waste of effort unless you can find something looks really nice on your wall. I think all the acoustical stuff may be deadening the sound. My basement wall offers lovely texture from a plaster cement finish and that's an amazing place for the system but the ceiling height is 7 feet, the materials that were used the ceiling tiles compressed board fiber material have done really well for me. Maybe remove some of the acoustical stuff.
Maybe the rear speakers should be closer to the back wall with a gap of three or four feet.