I had a room similar to this at one time. It was not easy to set up but what worked for me was using the Audio Physics method of speaker placement. It may be worth looking up and trying out. Almarg has suggested similar points in his post. Unfortunately you do not have a long wall but the system can still work with some modification. Put the listening chair within a couple feet of the back wall. Heavily treat the back wall, preferably with 4" panels. Then try moving your speakers into the room. In my set up they were half any in, but I also found that by moving them back towards the front wall in small increments that a third of the way in worked pretty good as well.
Another method you could try if it is feasible with your space is to use an off axis diagonal set up. If you visit the Decware website there is some good information on how to set this up. If anything you'll learn a lot about speaker placement which is not a bad skill to have.
Another method you could try if it is feasible with your space is to use an off axis diagonal set up. If you visit the Decware website there is some good information on how to set this up. If anything you'll learn a lot about speaker placement which is not a bad skill to have.