I personally don't feel my iPhone 3G needs an amp because headphone out is so good, but if you do use an amp with it, then it makes sense to use one that sounds better than the the built-in amp. The E5 with iPhone and line out dock is not going to be an improvement in sound, although it does offer more power. However, I was surprised at how much better the inexpensive E5 sounds vs the E3 that I bought my son. But in comparing the E5 to the iBasso T4, I found the T4 to offer more detail, ambience and soundstage - it was just as big of an upgrade over the E5 as the E5 was over the E3 (but the E3 takes away from the sound and should be avoided). Even then, an iPhone 3G can play my HD600 to medium volumes very cleanly and transparently, just not to loud volumes. So I just say no to an amp when I don't need it.