Direct USB computer to coaxial outboard DAC


I am looking for a way to bypass a sonos or apple TV. I want to know if there is a cable that goes from computer usb to either a coaxial or toslink connection in outboard DAC? If not possible what would be a cheap alternative without sacrificing sound quality?
beerad
I already have a DAC with coax and toslink inputs. I am trying to avoid buying a new DAC.
Thanks
I was not clear, I guess what I meant was it would prob be easier to get a new DAC. I believe any conversion process would prob degrade the signal quality.
Here is another vote for the HagUSB. I have compared with the M-Audio transit and some Generic PCI soundcard, and the HagUSB is my preferred route. You can find more favourable posts here on Audiogon, if you do a search.

Good luck,
Soren