[basementjack]

Well one nice thing is, since the walls are sloped, I think you could get good milage out of some form of corner traps down where the walls meet the floor.

If they slope to a point, then go straight down, you could shove a ton of insulation in that attic space.
I would expect the room to have decent low frequency response. due to those characteristics. So all you should have to deal with is echos.

Have you downloaded and used REW before? It would probably be a good idea to measure the room now so you know what you're dealing with in finite terms...