Bit of an invalid test since the files played through both players were not-identical. The iPhone had tracks from iTunes, the Pono tracks from the Pono Store.

Any difference in loudness will give the edge to the track which is mastered at a higher volume. That's precisely why tracks are mastered to go louder - it helps sell records but unfortunately on any half decent hifi sounds like mush: http://www.leonroy.com/blog/2013/04/buying-hi-def-music-toda...