Convert Vintage Audiophile CD Player (Mod Squad Prism - CDB650) to "DAC"

I feel pretty confident this is not a new or novel concept, but what I would like to try to do is find a way to bypass the transport, and feed my old Mod Squad Prism (modded Magnavox CDB650 + I also have a stock CDB650) with a digital stream, and effectively use the old CD Player as a DAC.

Can anyone please point me in the direction of finding out how to do something like this?