I tried out the HD600 about a week ago, simply to compare and contrast against the HD650. The interesting part is, I can just barely tell the difference. It would be very hard for me to correctly pick the right one if I was blindfolded and someone switched back and forth between the two. Maybe I just don't have much experience comparing headphones as some others, but they really are that similar to me. To my surprise, the bass on the HD600 is much the same, although with extensive testing there is a tiny bit less sub bass. And the treble really doesn't sound any brighter to me than the HD650. I really never understood why people describe the 650 as gooey and too warm. Now, I did recently put brand new pads on the 650, and if I did a comparison with the old pads, I'm sure my impressions would be hdifferent. The new less compressed pads on the 650 make them slightly brighter with less bass hump, as measurements suggest. So for me, them being so similar, it's not worth keeping both and I decided to keep just the 650.