It is supposed to be that way since the ATH M50x does not need a Amplifier in most of the situations, hence you won't be able to see a difference, you should try it with earphones like the Philips SBH200
E06 It's very low end amp..
You'll loose sound details in lieu of amplification.
M50x doesn't need a amp in most cases so you're better off without a cheaper amp like E06.