These are speaker level outputs from the receiver and the soundbar needs a digital output in optical form. If I have described this correctly above I would start anew. This seems difficult to achieve and many better options should be possible like ditching the soundbar with its limitations.
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?