I'm no "expert", but having played with a variety of room treatment options, including carpeting or Sonexing wall sections, over the years I'd be leery of carpeting entire walls. Doing that will suck out the natural liveness that's both present in recordings and contributes to the illusion of "realism" we strive for with our playback systems. At the same time, it's too thin to help with standing wave modes. I hope I don't offend anyone in saying so, but based on my experience I consider wall carpeting a "cheap suit" approach to room treatment.
I've found that combining diffusion and absorption when treating a room better preserves what the recording engineer has managed to capture (and perhaps enhance). You've already trapped the corners. Instead of carpeting the walls, try a combination of diffusion and absorption at the midwall positions on both the long and short walls and at the first and second reflection points. That way, you'll take care of the major room modes and provide a more naturally ambient environment to "load" your speakers.
Jim