I feel that the highs on the RS1i are nicely extended, articulate, fast, and euphoric. The problem I came upon occasionally was the peak in the lower treble/upper mids. Due to the said peak, it causes a narrowing of the sounds stage for me as it takes away from a more desired linear presentation of the these regions (upper Mids & Treble). The Mid Bass rise doesn't help either. This will also lead to premature listening fatigue for me. The GS2Ke has a more linear mid to treble transition while avoiding any offensive peaks in doing so with no mid bass rise either. As a result you are able to enjoy greater detail with an expanded soundstage and no irritating peaks. On a side note, these "peaks" are probably more of an issue for me or more noticeable as I only have listened to/use solid state amps.
I feel that the RS1i's are a detail oriented headphone with a mid region emphasis. I LOVE this presentation but I have found that this is not a neutral presentation and as a result colors my music. The GS2Ke is very linear and airy to my ears. To my ears, the GS2Ke is a clear upgrade and not just a different sonic flavor in regards to the RS1i.