I've recently bought the Beoplay H6 headphones, which I use sometimes with my 6 Plus. I found the audio quality to be a lot poorer on the phone than the output I experienced with my custom IEMs. I then tried the H6 with an old 6th gen nano (same track, bitrate etc), and the quality difference was just unbelievable. Much clearer mids, more depth, higher clarity. Now the iPhone 6 Plus is supposed to have great DAC so I'm not sure what's going on here. Any ideas?