Got these today.
It's a RE262 upgrade for sure, very similar signature, midrange focused with soft treble and bass.
RE272 upgrade? I can't compare them side-by-side, but the RE272 impressed me quite more, despite taking issue with it's bass. At most it's a RE272 sidegrade. RE272 is clearer and more airy, even though it wont have the 400s "sweetness". Will compare them side-by-side to RE400 soon, will mod RE400 to match RE600 and compare as well.
They don't stand a chance to my BDD+NE or my modded 9927..
More details later.
I have to say, the first thing that came to mind when I heard the RE-600 for the first time was RE-262, the description of signature just about matched up exactly despite me never hearing the RE-262 (reason why I didn't say anything). I will agree with softer treble, but can't say it has soft bass, IMO, it's at the same level (quantity-wise) as the RE-400 (unless you consider that soft, then I'm in complete agreement).