I just said I find this to be VERY untrue. I have tried it and no new sounds discovered, no benefits at all as there should be none in theory. "it is another world completely" "becomes another iem totally" "discovering new sounds you didn't know existed" nope, none of that happened in my case, so I just wanted to give friendly advice to people reading this thread not to spend money on extra amp for this super sensitive easy to drive earphones, but then again, we all have different opinions and experiences, obviously.
Now if original source amp is a complete disaster probably external would help as castleofargh said even on iems such as IE80, but for my X3 (and X5 that I've tried) there was no benefits on IE80, just extra device to carry around and extra money spent for a device that you not only don't need but that will make your pocket heavier, even tho you will look "more audiophile" when you take it out in public.
This is just my opinion based on my experience, other people either want to hear or really hear HUGE differences, but at least try it out before buying!
This echoes my experience.
Love the "looking more audiophile".