Stupid question, but what exactly do you do with those? Plug them into your computer and amplify sound volume through them instead of your speaker knob / windows volume?
It's a DAC and an amp. Simply put, the DAC acts as a much better soundcard and the amp acts to allow the DAC to output sound to your headphones, as the DAC usually lacks enough current on the output. Said amp will also separate the load of the headphones from the circuitry of the DAC, which is important for load balancing (impedance matching) and proper grounding.
It also has a tube in it because lots of people prefer them.
If you're interested in learning, I can point you to some literature. Rane has some good stuff
http://www.rane.com/library.html#gpm1_2