line 17 on the single shot example:
// Setting these values incorrectly may destroy your ADC!
This is not true. You can set gain to whatever you want, you cannot destroy your ADC, only clip your readings with the gain setting.
The "do not exceed VDD +-0.3v" is true. But if you are using 3.3v, that means 3.6v is the limit, no matter what gain setting.