Hi, I am looking to buy my first headphones. I researched a lot and thinking to buy DT-770 Pro 250 ohm version. But i am not sure weather 250 ohm headphones will work with my asrock z77 extreme4 (ALC898 onboard audio chip). I really do not want to buy amp. I want to also use headphones with my nexus5. Will i be able to use them with phone? Can someone explain headphone impedance importance and how it works in easy language? I read about impedance on google but i am not intelligent enough to understand it. Does amp only make sound high or it improve the overall sound quality?