Yes DX160 is a great pairing with the EM10, this DAP pairs well with about everything anyway
I never use EQ as a general rule, and I am always on low gain DX160 is powerful that way
I didn't need to buy the HR cable as it's now included with the EM10 so I own it and yes it's a nice cable...Yes you would notice a difference the former cables were really so so...
At this moment I have as it came the settings, Yes note if quite a difference with the "gain" on or not. But find a good investment compared to what I have in my velvet? As it is still 100 €