Last year, I purchased the NuForce uDAC-3, a mini DAC/AMP combo, from Massdrop at ~$80. I had some difficulty searching for the necessary equipment to use with it (cough cough coaxial cable), but after some weeks of having it, the DAC/AMP finally began functioning. WOW! The audio tracks on YouTube that I had listened to previously had more clarity, tighter bass, and higher listening volumes. Together, the uDAC-3 and my AKG M220 Studio Headphones (Thanks Massdrop ;) ) are killing the audio game.
To everyone first exploring the possibility of owning a DAC or an amplifier: I would seriously recommend the NuForce uDAC series as a starting pick!