I would try absorption over diffusion. I believe an acoustic panel on each side wall, even if not ideally placed as to 1st reflection, and base traps in corners behind speakers would help. In addition, you will have done something which seems to be a need for you. Check out ATS Acoustics, I have made my own panels and base traps from their supplies.
I am still having fun experimenting with my listening room.
Regards, Mike
I am still having fun experimenting with my listening room.
Regards, Mike