Blueskiespbd - have you an update on your "brightness" problem?
I added a QRD diffuser to the side wall to treat the 1st reflection from the main speaker on the opposite side of the room which reduced a bit of HF glare while improving musical details. So, using a miror I found the spot on the left wall that is the 1st reflective spot of the right main speaker and vice versa for the other side wall, and placed a 2ft wide diffuser there at ear level. Worked well as would a thick absorbing panel. You might try it.