[antonyfirst]

I've not listened to any amps (though I'd love if someone loaned to me an iMod + amp), but I would say: definetely so. The ER4 give me the impression that they can grow much more than the E500.
To use an analogy, the Etys are like an empty box that can be filled with more and more goodness, while the E500 have their own goodness, and don't change much their sound signature (whatever eq settings I use with them).