I've been using an E5 for over 2 years now, originally with an archos 5 and now with my htc desire for the last few months. I guess the answer to your question depends on your headphones. I'm using with head-fi RE0 - brilliant earphones but quite a flat treble/bass response. The E5s have a wonderful effect on these - increase the soundstage, give enough oomph to the bass to really enjoy trance/house. Jazz/classical sounds amazing. By the way I'm using spotify premium for all my listening now. The connections are just standard and mine fit fine with the Desire. In fact I have bought a mini-usb to micro in order to use the E5 charger on my phone. Only niggle is that the E5 will very occasionally pick up inteference - it is not fully shielded (and I've had 2). Only seems to happen occasionally when someone sits next to me with a blackberry on the train. Anyway the sound improvement far outweighs any negative impact. I can't do without it!
