I'm not sure that any special room treatment is really needed for Magnepans vs most other types of speaker... It is best however to set Magnepans 3 to 6 feet out from the front wall if you want to maximize the soundstage depth. The Rule of 'Thirds' is a good start; one third into the room from the front wall and one third into the rooms width. If your room is too square (or cubed) then some bass traps may well be needed. What are the dimensions of your room?
Use a reasonable balance of diffusion and absorption throughout the room; too much absorption and you suck-up all the detail. I personally like as much diffusion behind the listening position and on the ceiling as possible. You don't have to use fancy (expensive) RPG panels to get decent diffusion (though the real thing does work better), book shelfs loaded with records or CD's work well too.
Use a reasonable balance of diffusion and absorption throughout the room; too much absorption and you suck-up all the detail. I personally like as much diffusion behind the listening position and on the ceiling as possible. You don't have to use fancy (expensive) RPG panels to get decent diffusion (though the real thing does work better), book shelfs loaded with records or CD's work well too.