As for remote control, I considered this awhile back and thought of using a multiplying current DAC instead of a digital potentiometer for control. A 14 to 16 bit unit would be ideal. You want a unit without a built in reference. I actually drew up a circuit using an LT part and successfully simulated it, but never got around to trying it out. I can dig up the circuit if you want.
The problem with using a digital pot is accuracy and linearity. Ultimately, you could use a digital pot, but you’d need to add an ADC to read back the voltage and implement closed loop control in software. With the DAC method, you could do without the ADC by implementing a lookup table of DAC codes vs power supply output voltage, since you’d have more bits to work with and better linearity.
The other problem with a digital pot is compliance voltage. Most have a 5V limit, which is well outside the 20V you’ll need with the power supply. Higher end current DACs can do 30V or more.
HP actually used to make a “Power Supply Programming” box for their older power supplies that were remote programmed with resistance, just like the Power Designs supplies. It was essentially two multiplying DACs with a GPIB interface. So the idea is sound. Remember, a DAC is nothing but a network of resistors.