Panels to treat a vaulted ceiling?

My listening room is 16x23 with a vaulted ceiling, hard floors, hard walls and sometimes hard to listen to. I listen across the short side of the room using only 2/3 of the width leaving the highest part of the ceiling about a foot to the right of the right speaker. Book shelves and a large rug have tamed the floor and walls. All is well at low listening levels but how do I control the ring and echo that 400 square feet of ceiling produce at high listening levels. This is the only room that gives me a problem. I saw the spell check thread a while back and hope I have not misspelled ceiling a half a dozen times.
Thanks for any suggestions.
You are probably better treating the floors (and possibly the walls) rather than the ceiling. I have a similar room. Is the ceiling higher above one speaker than the other? Can you place the system on the wall under the low end of the ceiling so the speakers are firing down the long end of the room? This will provide better balance and maybe less trouble with reflections.

At one time I had my system set up similar to what I described, and it sounded much better after I moved it 90 degrees to fire down the length of the room.

The ceiling is 2-3 feet higher above the right speaker. I would like to move it to the short wall but this would not please my boss {wife}. Thanks.
I have very similar room and ceiling issues and have found that the most effective way to defeat reverberance is with floor-to-ceiling tube traps. This is not likely to be an option for you, but an inwall treatment like the Corning system may work. The ring is flutter echo, and usually occurs between the floor and ceiling at places where the floor is uncovered hardwood. You can place absorbers (more rugs) at those points, or better yet diffusors, once you have identified the surfaces responsible. I was able to cure a considerable amount of ring by placing a 3'x5' rug on a part of the hardwood floor where the ceiling was focussing energy.
You might try RPG Skylines. They can even be (spray) painted to match the ceiling. I don't have them on the ceiling, but I liked their effect behind my listening position. I also found that RoomTunes corner diffusers are an inexpensive improvement. I think EchoBuster makes something similar. If you fear this kind of death-by-a-thousand-cuts approach, go for Tube Traps, which fix anything, but they are expensive.
another comment after my above post -
Don't buy anything until you have diagnosed the problem. If you equip yourself with strips of material e.g towels, rags, or even cheap foam pads of reasonable thickness and spend a day taping it to various parts of the walls, ceiling, and floors, you can zero in on what surfaces produce the echo and ring.
It's also worth checking what the effect is of putting proper bass traps in the room corners, particularly front corners. Can help with bass reverb. They can be made inexpensively (aa links) or borrowed for the purpose.