In this kind of setup, you could connect the headphone output of your computer to the mini-stereo input of the HD6s or you could use an external USB DAC, like our D1. The DAC built into the HD6 is solid and really helps make sure you get a consistent experience.  With that said, DACs like the D1 would bring you extra features like a dedicated headphone amp or easily accessible volume knob; this could also free up the optical input to use with another source, like a television, if you want. You can check out the D1 here: