I've connected N810 headphone out to my C&C Box+ headphone amp which is connected to my Beyerdynamic DT770 Pro 80 Ohm. Sound quality improves drastically, and hiss is gone. very happy =). Note: volume on max is usually equivalent to a line out (on some players yes, some no).

edit: just tested with JBL Reference 410. Hiss reduced drastically as well, more punchy. I will try Crossroads MylarOne X3, JVC HA FX66 later on (sleepy).

An amp might help if you dislike the hiss. Not sure if all amps will do so though. For reference, I have a C&C Box+ headphone amp upgraded with an LTC6241HV op amp.