It's the same reasoning with DAC's. Do I really have to clarify everything?
The E9 is all power. It can drive any headphone that exists today. Headphone amps exist to amplify headphones and not to enhance sound in anyway.
Just like how DAC's only perform one function.
So what's the point in buying more expensive amps? I don't expect a straight-up answer from you but I bet someone else here will answer that for me.
Besides most opinion's on the E9 are positive. That being said I don't care what others think but you seem to care so much about other people's opinion.
Why have you bought an amp at all? This is a special device and there are enough more practical devices with a headphone out..