PMP & IEMs - worth an upgrade?

[Podie]

As a seasoned train commuter, to bloke out the idiots I listen to music. Having noticed that with each generation of iPhone the quality of the same MP3 was sounding worse I treated myself to a PMP and IEM combo at the end of last year.

I'm currently using a Fiio X3 with Shure SE425s (and Westone Star Tips) and I've thoroughly enjoyed my (lossless) music again.

I'm now listening to more and more music and wondering about a cheeky upgrade to either the PMP or the IEMs - can't justify both at the moment.

So, do I go for the X5 Gen 2 - or should I be looking at some Shure SE535s?

Musical tastes are best described as "guitar based rock" - whether that's Floyd / Led Zep or Soundgarden / STP or RATM / FNM.

Suggestions welcome.