At 140 or so hours, I noted the same problem Edgar Kramer observed at 100 hours. Everything fell apart. It was not as bad as out-of-the-box, but really muddled. Now, at 250+ hours of burn in, what a wonderful set of amps. Fabulous in all levels of performance, but most importantly they are musical. I love them. I predict you will not find many, if any, on the used market. Maybe if the Reference 18s hit it out of the park?
NuForce changed the faceplate on the upgraded amps from the new ones, but so what? I will not be selling mine in the foreseeable future.
Mark