Audio ADC - grounding problem
You don't have a problem. The audio is AC coupled to the PCM1803 chip input, just look at the example schematics in the datasheet. The PCM1803 applies a 2.5V bias to the input analog signal so that it doesn't go below 0V if the 3Vpp condition for the input singal is met. AC coupling capacitor ensures that the 2.5V bias does not interfere with the audio signal source.
I would not use the Maxim part for audio.