It looks to me as though your room has a large volume (the rear wall is open, the left wall is distant from the left speaker) but early reflections. (No wonder you have a big subwoofer.) The more first reflection points you can treat, the better.
The right speaker cries out to be moved away from the wall, but obviously there's not much room to do that. An absorbent panel could be placed either on that wall (to the right of the right speaker) or in the corner (where it could do double duty as a bass trap if properly designed). Given that you can't change where your system is placed, I would look into treating that wall and corner first.
Have a look at Jon Risch's acoustics pages to get an idea of what's possible.
http://www.geocities.com/jonrisch/a.htm
To see if it would help to treat that corner simultaneously for bass-region modes and mid-high diffusion, try a quick-and-dirty test. Buy or borrow a large sealed plastic bag of insulation (fiberglass, rock wool or other), place it in the corner behind the right speaker and do some test listening. Obviously you won't be able to leave the bag there--you may even have no other use for it and have to take it back to the store for a refund afterwards--but if you do have anything to gain from treating that corner, it should show up.
The right speaker cries out to be moved away from the wall, but obviously there's not much room to do that. An absorbent panel could be placed either on that wall (to the right of the right speaker) or in the corner (where it could do double duty as a bass trap if properly designed). Given that you can't change where your system is placed, I would look into treating that wall and corner first.
Have a look at Jon Risch's acoustics pages to get an idea of what's possible.
http://www.geocities.com/jonrisch/a.htm
To see if it would help to treat that corner simultaneously for bass-region modes and mid-high diffusion, try a quick-and-dirty test. Buy or borrow a large sealed plastic bag of insulation (fiberglass, rock wool or other), place it in the corner behind the right speaker and do some test listening. Obviously you won't be able to leave the bag there--you may even have no other use for it and have to take it back to the store for a refund afterwards--but if you do have anything to gain from treating that corner, it should show up.