IDK about the RE2, never had them, but the Etys have the best isolation i have ever heard from any universal fit IEM. Etys will do fine for rock, but may lack behind on electronica because it doesnt have huge quantities of bass
Having heard both (I owned ER-6i for a few months, and two of my labmates have RE2s on my recco), I'll say that RE2s don't isolate well relative to ER-6i. Indeed, I'd say they don't isolate well period, but that might be a little unfair.
I don't many other ear phones that can beat the isolation of the er-6 series. For my ears, they fit quite deep but they are the easiest IEMs for me to insert and pull out. The only thing I have with better isolation is my UM3x with the standard comply ear tips.
The only downside of the er-6 is the bass response and overly analytical signature.