Both.
It would be better to use a series resistor plus two diodes. Connects resistor to the output pin of the Opamp and the other end to the CS5463 input, and diodes from CS5463 pin to VA+ and 0V respectively to limit the swing of the possible input voltage.
This is a common and effective means to limit the swing of input voltages between the power supply and 0V of the down stream CS5463 IC. Since the inputs are CMOS with impedance of min. 2Mohm, you can try 100K and two 1N4148 silicon signal diodes. You'll need to repeat this on the other input pin.
Correct. One wants sufficient supply headroom on the opamp supply so that it can perform its job more effectively.