I doubt these are what you want, but I don't think a simple converter like you want exists
http://www.thewelltemperedcomputer.com/HW/SPDIF-USB.htm
https://www.amazon.com/Creative-Sound-Blaster-System-Preamp/dp/B004275EO4/ref=sr_1_1?ie=UTF8&qid...
http://www.thewelltemperedcomputer.com/HW/SPDIF-USB.htm
https://www.amazon.com/Creative-Sound-Blaster-System-Preamp/dp/B004275EO4/ref=sr_1_1?ie=UTF8&qid...