Do you not have a sound card on your computer with a optical output. I connected my Benchmark DAC3B to my computer this way. This is not the ideal way to listen to music, but OK for watching my hockey and baseball games via the computer.
For music streaming, you could consider the Denafrips DDC products that are supposed to be good quality and relatively low cost. This will solve your connectivity issue to the Benchmark DAC1.
Here is the sound card I use on my computer. It was supposed to be good back in the day.
ESI - Product Archive: Juli@ (esi-audio.com)