I have not specifically treated the ceiling, and think that would be a tough to sell with my chief decorator/LOML. However, there’s a textured ceiling, and two ceiling fan structures that may help with some diffraction....perhaps I could suggest a couple of well designed decorative medallions around them.
The floor was easy, with thick wall to wall carpet. The suspended floor underneath...not so helpful, but I bet I could get away with a few extra lolly posts in the crawl space below.
It's not ceiling/floor, but the large fireplace structure on the wall behind the speakers seems to offer some diffraction help. I’ve been bugging her about installing some book cases to further enhance that effect. We shall see!