You've dampened the room, but your biggest source of brightness is the first reflection off the floor from the mains. Sit at the listening position and have someone hold a flashlight next to the L&R speakers. Where you see the light reflecting on the floor is your primary reflection point. If...
I'm not sure there's a lot more you can do. It's a hard wood floor? You could try a floor covering at the direct reflecting point between the mains and the listening position. I know a lot of people try to set up rear surrounds when you're sitting against the back wall, I'm just not sure it...