@jkampmeyer I can confirm I have used a solution like @gkelly suggested, going from RCA to optical for a wireless headphone system, and it did work. Quality was within expectations for such a setup.
RCA to Optical Converter
I have an older Onkyo TX-8050 receiver. I want to connect the speaker output (left & right, each with a red & white RCA female connector, total of 4) to my Bose soundbar. The only option I have for input on the soundbar is an optical female. How do I do this?