I don't have the E4C, but I do have the IM716....IMHO there is a huge difference in the IM716 with & without an amp/QUOTE]
Excellent point that I forgot to mention - no question that the IM716 sounds better with an amp. In fact I would say that if you didn't have an amp you might consider looking elsewhere (at least that's my experience straight out of my 5.5G IPOD). I still think, even with a good amp that they're lean on the bottom end.