the E10, like most other IEM's, are designed to be drived from a PMP, as generally many people doesn't use amps with MP3 players.
That's why the E10, again, like most other IEM's, have low impendance and high sensitivity.
The high sensitivity is what makes your E10 hisses with the E11.
The E11 itself is pretty hissy, coupled with a sensitive IEM, it will become more audible.
I suggest using the E10 straight away without the E11, because it's efficient...