ok here's where i have a see a few downsides...
the headphone support is kind of... hmmm
firstly you have to select "HP" from "LINE"... so the socket isnt live until you turn it on with the menu... sure why not?
2nd it doesnt have enough power... I'm at vol 35 with a max of 40... this is the Bowers P7 which I never found to be all the power hungry?
I also tried my Bowers PX5 and my AKG NC700 and its the same story... I dont think it sounds all that good either... unlike my dedicated units like my Xduoo XD5.
BUT I mean you have to expect a dedicated unit to beat whats a 'freebie' on a desktop dac. Its not good, not terrible... 3.6!
You are using low impedance headphones and are difficult to drive.
Try using the balanced headphone output. it will give you much more power than single ended.
Yes the headphone output comes directly from the chip and is pretty weak. But as long as it's not clipping for your headphone, it should sound good.