You will have to be a dab hand at soldering, knowledge of the ciruitry and the ability to create the new circut board with the input paths if non existing and so on and so forth.
Not to say it hasn't been done, but go to such expense, time and effort to do so i would of thought none wouldn't bother to go to such lengths and get an ext dac or replace the cdp with one that has digital inputs if that is their desire.
If they have time on their hands and just experimenting to see if can be done then more power to them
BTW, never knew PT dabbled in Cdp's. Learn something new everyday.