I went over what I know about the ADC in another post:
The peak to peak full scale input is around 1.6 volts as far as I can tell. The input impedance varies from 6k to 30k depending on the gain setting. For a line level input you’ll want to use a low gain. You should AC couple the inputs.
Set a very low output gain then vary the input gain to find the right level (so you know any overload comes from the input amp).