Buy a dozen 6' artificial ficus trees and place a couple behind the speakers, between the speakers, nest to the speakers to diffuse wall reflections behind your listening position and int he corners behind the speakers. Last I looked these artificial trees were $40 each at the At Home store.
These artificial ficus trees act as very effective diffusers. They are easily moved and can help "fix" a room.
You can add more (I'm up to around 18).
That's a start, and a LOT cheaper than audiophile room treatment.