Convert Sony SCD-XA777ES into DAC

[Sony]

The concept is simple. I need a DAC for TV box and game console (both PCM signal 16bit/44.1KHz), and I have a SONY SCD-XA777Es SACD/CD Player that has a nice DAC inside. So I want to use it as a DAC while preserving its standalone player function.

So, in theory, I need to add SPDIF digital inputs on the back of the player (plus a switch to commute modes - internal or external conversion). On the inside I must convert the new external digital signals so that it's compatible with the CD signal before the oversampling/upsampling filters, and connect the signal there with a commute device operated by the external button.

Does this make sense? Is it doable? Is it worth the try?

The diagram illustrates the idea: