Here is something that will take a USB input from your computer and convert it to toslink or SPDiF without performing DA conversion for $79 ----
http://www.computersandmusic.com/xcgi/SoftCart.exe/store1/edirol/ua1a.html?L+mystore1+urub1816+1088598294
http://www.computersandmusic.com/xcgi/SoftCart.exe/store1/edirol/ua1a.html?L+mystore1+urub1816+1088598294