I have a fairly narrow familiarity with the full line, but what I like about my RS1i is that it sounds good w/ so many genres including metal. But, it sounds good with just about anything I throw at it. Not a big classical music fan, but an appreciator...and I think it actually sounds OK especially smaller ensemble classical. And, fantastic with anything acoustic like jazz. May not have the bite some would want for death metal-but less fatiguing than my 225i which I still think is a great sweet entry spot for rock and metal. The RS1i tames the treble down, is still very good w/ metal but adds a touch of refinement for other genres. My 2 C.
That said, I have yet to buy high end big boy planar headphones as I've been working on creating a listening room/computer space (newly painted with some new furniture) and upgrading my speaker system...like a devious wizard (electric wizard perhaps) it's slowly coming together. I'm getting close!