Matching Looks when using that combo rig
Analog Bass Boost
And maybe even a bit more of a refined sound in the E12. I have the E12, but haven't done a formal comparison yet between the two
So the points I can mainly think of would be that the E12 is an amp for those that want to driver bigger cans with the X5 and wish to stick with FiiO. And or want the slight sonic changes the E12 offers.