RCA to Optical Converter

No guarantees 

https://www.amazon.com/Digital-Converter-Hdiwousp-Aluminum-Headphone/dp/B0863F49PS/ref=mp_s_a_1_2_sspa?adgrpid=174874538125&dib=eyJ2IjoiMSJ9.x0RYVSUNcVpInxANAaY0bdR1GHfCrxzbmipq0zoMR7OJV4gVzuTpbbcES7_CIXmvUeabThFMbY3NFmx_HL1jNKuVAbx03rstLTXxwnfYH7vAocAttenHqU4NBBXCPQzKT-2U8iyJh7Z6opqWEo6Ae-yLkQoazdQTbBnmBkha9qSEBtjcbUqPbK7xYJSG-DXm5BOhzBNksEJtQ-u36dR9Pw._oeoZrrVBlsBveQvAC_YSRH7UomHoZvWsVJQsCw6F-c&dib_tag=se&hvadid=739151557381&hvdev=m&hvexpln=68&hvlocphy=9033780&hvnetw=g&hvocijid=4755859377969492446--&hvqmt=e&hvrand=4755859377969492446&hvtargid=kwd-306150123533&hydadcr=16190_13526812&keywords=analog+rca+to+digital+optical+audio&mcid=b4b5ba811ec534e4a15c85c3a9ec90bd&qid=1753828347&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9waG9uZV9zZWFyY2hfYXRm&psc=1

@jkampmeyer 

Also, you would need to use the "Pre Out" L/R outputs into the Digital converter that @gkelly posted. 

And, with not completely understanding what you are trying to accomplish, remember, it will only be a stereo signal into the soundbar, so if you will not get any kind of surround sound.

@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.

My challenge is that each of the speaker outputs has a red & white RCA female jack (a total of 4) I cannot find a DAC that has 4 RCA inputs. Also, I don't think I need a preamp, as my receiver has a phono input.