Well...amazing pretty much sums them up. And I'm not even using an amp at the time. Just straight out of my iBook. I probably won't be getting one anytime soon. Can't justify spending $100+ on an amp or a DAC.
I am really sensitive to the sibilance that my MS-1 and Goldrings had. Irritated me so much. One day, I snuck a listen to someone's lower end Senns (like the 2XX models). No sibilance=fantastic in my book. I could care less about the slam of the bass or the extension of the highs if the sibilance was there.
I listen to a lot of mainstream music (pop, r&b, rap, rock), audiophile stuff my dad finds, and just random stuff from everywhere else. The bass totally rocks on these headphones...excellent extension and slam. Probably not as tight as they could be, but considering that I don't have to deal with placement and calibrating a subwoofer for speakers, it sounds pretty darn good to me. No noticeable peaks as the Goldrings have in the upper bass. Highs are a bit rolled off but I don't listen to enough of classical/stringed instruments to notice. Mids are lovely: smooth, detailed, NO SIBILANCE!!!, full bodied and rich. Instrument separation is excellent. I can pick out ANY instrument in the song and just follow the panning and melody. Soundstage is not 3D yet as I've heard some speakers do, but better than any other headphone I've heard.