I'm curious as to what sets these apart, really. I found a 400 that had 6550's in it, and was told that it reproduces the same amount of power as the 12 6L6's in the 400+. Don't know if that's true or not, but heard it. Anyhow, I found some good deals on the 400, but didn't know how different it was. One thing though I really like about the 400+ is the ability to go to 2 ohms, which the 400 can't do. But other than that, anything else?