Another strange comment about the 600. The mids/vocals are more up front than any other mid-fi phone I have tried. Actually none of the other phones I have owned besides the Grados have even been close to the vocal presence of the Sennheiser and why I have never found a replacement for them. You are spot on regarding imaging and soundstage though. The treble is rolled off a tad soon for me too, but the way they did it gives excellent timbre up high and this is where most phones fail. I understand sound preference is subjective, but I can't own phones that don't sound like live instruments and Senheiser is the only one I have found that has accomplished that.
I was referring more to the 650 than the 600 about vocals sounding distant. It's not rather that the vocals are distant, but rather the bass of that headphone overshadows the midrange. I also wish the 600 had more upfront vocals but it has a more balanced frequency than the 650 from what I've heard. Timbre on both headphones are great.