Ccanino,
Adding to the room treatment remarks made by Bryan and Ckoffend, I might suggest you temporarilly take your side wall 1st reflection absorbers and move them to your back wall (behind the listening position); reflections from the back and front wall are more troublesome than side walls and ceiling due to the lower angles of incidence which reduces apparent source width and spaciousness.
Diffusion - either 1D or 2D - on your back wall works well depending on your sitting distance. Note that the diffusion coefficient depends on the angle of incidence of sound, with the greatest diffusion occurring at 0 degrees incidence, and because of the lower angles of incidence from your speakers to the back wall, diffusion can be very effective in helping to add "listener envelopment," a positive thing.
Many people mistakenly walk in a room, clap their hands and hear slap echoes not realizing it does not accurately represent what they hear from the loudspeakers when sitting down in their chairs. Slap/flutter echos will be most audible with short transient sounds - and probably inaudible with sustained music. Be sure to have someone stand next to or over your speaker and clap their hands while you listen from your listening chair to detect whether flutter echos can be heard there or not.
Good luck and keep us posted.
