SPDIF to USB Converter?

Hi Everyone.  I have the inverse situation from the one that I see discussed in many threads.  I have an Anthem pre-amp/processor which has an SP/DIF output but no USB output.  I am interested in using this to rip my LP's for use in portable audio, but none of my computers have an optical input (all the old ones have died), so I have been searching for a SP-DIF to USB converter (I can;'t find anything on the used market, which would be fine for this use).  If I had a Wayback Machine, I could go back about 10 years and find a slew of them and my computers would probably have the inputs as well.  I wonder if anyone has a simple (i.e. cheap) solution; I am capable of a certain amount of DIY if needed.  At some point I will invest in a simple A/D converter, but it seems like a waste to have an A/D already in my system and not use it. Thanks in advance for any suggestions.