Arghh, my S2 just died. It sounded a little strange for a few hours, and now it refuses to detect that an USB cable is attached (I tried restart, different cables, different USB inputs etc). So now I use my old DragonFly Dac, and will return the S2 to dealer for warranty fix (which will probably take like 2 months).
It has made me appreciate the sound from the S2 more though, changing to the DragonFly Dac (which is excellent for its price), was a big step down. Everything sounds flat and boring, and stereo image shrank a lot (no more playing outside the speakers).