[Weasel9992]

I agree with jwl...more bass trapping is required. I'm also seeing the possibility of some real issues n the back part of the room with the untreated walls aimed right into the floor. Maybe not such a huge problem at the listening position, but it would be a big problem for tracking.

Book cases don't work very well from a diffusion standpoint. If they're filled with books they'll partially absorb high end stuff over much of the surface, but reflect it from part. Even if the whole surface of the bookcase did act reflectively, it's not really randomized at all. The result in both cases is not diffusion...it's closer to comb filtering. If it's not filled with books, then each nook acts like it's only little resonance chamber at particular frequencies depending on the specific material and density.

I think you could add a good bit more treatment without killing the room.

Frank