I'll do you one better, not that there's anything wrong with the previous suggestion. http://www.ebay.com/itm/ELE-EL-D01-MINI-HIFI-USB-PCM2704-DAC-BOARD-CARD-ELNA-Capacitor-New-/120985506266?_trksid=p2047675.m1982&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D119%26meid%3D3857010348415227396%26pid%3D100009%26prg%3D1089%26rk%3D2%26sd%3D251075511946%26
An ELE dac that use can connect with a regular printer cable if you don't wanna spend the extra couple bucks and get something more aimed towards getting the most out of your sound.
Simply put the ELE dac is a dac and amp, does a great job with both and will definitely get rid of that hiss will giving you a major upgrade in sound. I recently put in a order for mine given the reviews over on the discovery thread over in the IEM section. For 20$ bucks it seems pretty hard to beat