I just got some new 650s to go with my 600/700/800 Senn addiction collection. At meets it's easy to say the 600 and 650 sounds very much a like. At home I can confidently say the 650 is a more refined, smoother-ish 600, but not by too much but enough to instantly hear it. And yes, more resolving. Soundstage depth I dunno about.