I had this player too, robust made, snap disc reading.
After check schematic,
CDP 502 ES from cx 23034 ( digital filter ) go to SONY DAC cx20152.
With similar model maybe 502 or 552 esd, For transmit to spdif, it's need ic cxd1075P, digital interface format converter.
The similar model but with BB DAC pcm53, after digital filter, there is other ic cxd 1058Q, serial to parallel converter, before pcm53.
I m interest to this modification but i/m not EE back ground.
just my 2 cents.