Once again, the jailbreaking iOS 8 brings a solution! a very simple manipulation'll allow us to lift this restriction.
1.Use iFile (Cydia Free) or any other program that allows you to explore the tree of your iDevice.
2.Then go to the directory /System/Lybrary/Frameworks/MediaToolBox.framework/Default Edit
3.The RegionalVolumeLimits.plist file as follows:
Then make a respring your device ,
Attention prolonged listening to full-power music can damage your hearing.