Using one of these eliminates the hiss with my DN-2000J and DFR. There's a lot of debate on whether or not impedance adapters do what they're supposed to - increase the impedance of the headphones, not the source and vice versa - but it works for me. I use the 75 ohm one. http://penonaudio.com/3.5mm-Male-to-3.5mm-Female-Impedance-Adapter There's also a Dunu made version. http://penonaudio.com/3.5mm-Inpedance-Plug
I have an S6 and can confirm that Samsung's USB audio implementation of the Dragonfly is very quiet with stock apps. My phone's headphone out can get 40-50% louder on max volume than the Red using stock apps.