You should check out Earmax too...many people love them with Senn headphones. I have a Grado headphone amp and it also works well with HD600's, but it's not a tube unit (nor does it sound like one).
Need Advice: Which Headphone Amp?
Okay, so I recently purchased a pair of Sennheiser HD 600 headphones and now need a headphone amp. Can you give me recommendations? I have thought of the Antique Sound Labs, David Berning, Rega and Headroom. Are any of these are others good matches for the Sennheiser's. Thanks alot