6 x 4 is a pretty small room to record much of anything, but if it's all you've got, you have to make the best of it. Personally, I would stay away from any of the foam products and consider making your own absorbers out of Owens Corning 703 or 705. You can purchase sheets of it and cover them with fabric and they look great. Then you just need a way to attach it to the ceiling and to your walls. You'll probably want to treat all the walls since you will have alot of ping-ponging back and forth in such a small room. Good luck!
"I feel so miserable without you; it's almost like having you here." Stephen Bishop