An improvement would be to kill the first reflections from the speakers as seen from the listening position. Here is what to do... Sit in your "sweet spot" and have a friend take a mirror, like a full length one and position it along the left side wall. Have him move it back and forth the wall, with the mirror pressing flat against it. When you can see the left speaker in the mirror from the listening chair, that is the place where you want to apply an absorbant panel. Do the same for the right speaker. For the absorption panel, you could make one out of bed foam material, the egg crate stuff you buy at Wal Mart and put on a bed.
I like to also have my wall behind the speakers "dead" by placing the bed foam all over it and then placing a floor to ceiling curtain there to hide it.
Another trick is to apply small pillows in the cieling corners, helps soundstage and imaging.
These are some tricks that will have great effect. Hope this helps!
Mike Morrow, See my room at my site...
www.morrowaudio.com