I remember, the amps on the ibasso d4 and fiio e7 were frighteningly similar.
I tried my best to pick out true differences, but my ears couldn't. And I used over 20 different headphones in this test.
In my view, portable amping iem's is just a more 'headfi acceptable' way of equalising it. Little toys that are equalisers.
Now, if you want a good eq, then i'd say get:
- a player with built in good eq, like the cowon i9/s9
- a player that's rockbox compatible, like sansa's or ipods. This firmware gives a much better eq than stock.