How do I put a DAC to good use?

I have a Pass Labs DAC 1 that is not being used. I thought about selling it, but I think it's one of those components that's probably to hard to sell. So I thought why not stream music through it. I have a Mac with iTunes and a Airport Express, but the AE only has USB out. How do I go from a USB to any of the DAC 1 inputs, be it XLR, COAX or Optical. Is their a component that can go inbetween these two? Thanks for all your input.