Back in the day, 10+ years ago, the HD600 was praised to the heavens when mated with tubes. I don't read much about that today. Is it because most users today have an aversion to tube amps or what? To those who haven't heard their HD600's with tubes, I would highly recommend checking it out!
Because before 2003 there was no HD650 . And typical tube flavor is to warm up the sound , more bass body , tame the highs etc
(yeah i know that some tube design sound like very neutral SS amps , and vice versa , just wondering ) .