Fixed Xperia Z2 headphone volume -NO ROOT- 
You can increase your headphone volume on xperia z2 dramatically,before i used this method my volume was constantly on 100% because it was too low,and now it's on 60% because it is too high and the best of all is that quality is untouched.This method is very easy...First of all download app called volume booster.Now your walkman settings should look like on the pics i uploaded before you start using the app (I hope they did im new on this site and im on my phone lol) ok so go to walkman/settings/ and do the SAME settings as i have on pics.When you'r done with that take your headphones plug them in play some song,go to volume booster and and move volume button in app from maximum to minimum and without releasing the button move it to the maximum(your button should barely touch the minimum sound so do it fast ---> From max to minimum without releasing than to the maximum and release button,you will hear sound like you do when you press volume up for call volume) if volume after that sound doesnt increase do it more times until the volume isn't VEEERY loud.I do it every time when listening to song it's not hard as it sound you will get used to it,it will pay off trust me
Love my xperia z2 now ^^ (settings are in croatian but that isnt importnant just uncheck clear audio go to equaliser and max out evertything and turn on DSEEHX( CRUCIAL STEP)
