There do exist USB-to-optical converters that should work in a setup like this, though a product like this isn't very widespread. We don't really have any recommendations on a specific brand or model to use, but a quick Google/Amazon search should yield results.
Another solution is to use an external DAC, like our D1 24-bit DAC, connected to the USB port on your computer and plug it into either of the analog inputs of your HD6s.
Another solution is to use an external DAC, like our D1 24-bit DAC, connected to the USB port on your computer and plug it into either of the analog inputs of your HD6s.
