I remember hearing ages ago that fiio's tended to color the sound with some emphasis on the bass. I could be remembering wrong, or maybe earlier models did have that problem. Anyways it could also be the phone, I'm sure the vast majority of phones out there assume people will use IEM's, and so they don't put something that powerful in it.
Honestly though I think the only song I remember noticing a difference in on a PMP with my old M50's was Gorillaz's "Welcome to the World of the Plastic Beach" And that really comes down to the extremely deep bass in that song. And this was probably on my old Zune HD which although not as popular among audiophiles as earlier Zunes, it was still considered to have a decent amp in it.