Only the rear muffler. They suggested that I may want to remove the center muffler if it was not loud enough. I don't think I will go that route. It sounds perfect the way it is.
I'll try and get a sound recording of it later today and post.
It would be nice to hear from any other 400e/e420 owners that have replaced the rear muffler with Remus, Supersprint, etc and hear what they say about the sound/performance. I have no regrets going with the Magnaflow.