josiah.grovesYes, you can absolutely us the D1 as your DAC, then out to an amp. You can utilize USB or optical out of your PC into the D1. But it is a DAC only- You won't be able to power a 600ohm headphone with this.
josiah.grovesI've got this, but I don't have a pair of beyers to give direct input. The O2+ODAC combo is great and very versatile so it should be able to power those. If you have more questions, you should head to headfi.org and search for threads on those cans and go here: http://www.head-fi.org/f/7840/introductions-help-and-recommendations
Good luck and I hope you enjoy those beyers.