Start a song on the walkman and crank up the volume to max, then go to settings and tap sound:
Tap 'Sound Effects'
Stick to the above settings for the best result and tap 'Sound Enhancements'
Choose a EQ setting which you like.
Now tap the Settings tab, On this setting the volume is maxed up, but you can play around with it and check whatever you like best.
For me, this way the music is even louder then I can bare at max volume...