Gigabyte audio gain control switch

[Rychill]

So im getting a pair of hd600s and knowing that these headphones are 300Ω my initial thought was that i need an apm to go with it. My next thought was that maybe changing some stuff around on my mobo(GA-Z170X Gaming 6), i wouldn't need an amp. The problem is that i have no idea how the audio gain control switch or OP amp works, and both the manual and website fail to explain what these are, do, and how to use them, other than a couple vague sentences (or maybe i didn't look hard enough). What i wanted to know is if anyone has experience with using these two things and what i would need to do, or if i need an amp. Thanks