Nice review mate! I have a Mojo so I can get a sense of the sound via your comparison. I also use Android OTG as a source often and like you I find it quite up to the task. Heck I actually rather enjoy Apt X Bluetooth well enough for that matter.

Hey guys. I got the S6 and also purchased some Hifiman HE-560s. 
 
I'm using a balanced cable and I feel like volume all the way to 100 is not loud enough. Is there something wrong with my setup/system?