If I remember correctly I think Rtings is using the HD800S's frequency response (a headphone known for it's huge soundstage) as a reference for the soundstage "measurements" of other headphones. And while I think that you definitely can get an idea on the stage of a headphone with their measurements, it is not an accurate thing and you should use your own ears for that in the end. But yes, the HD600 is not that good of a choice if you are looking for an expansive stage and the SR850 might very well be "better" than the HD600 for that, just like Rtings suggests.