Indeed, the analog input block contains a stereo line input and a microphone input with mic bias. Either input can be routed to the ADC. The register field CHIP_ANA_CTRL->SELECT_ADC controls this selection.
In the other hand, the line input can be routed to the headphone output by writing CHIP_ANA_CTRL->SELECT_HP. This selection bypasses the ADC and audio switch and routes the line input directly to the headphone output to enable a very low power pass through.
The Table 5 and 6 from datasheet refer to the Audio Performance.
What you do mean with reference levels for this dB-values?
>> What you do mean with reference levels for this dB-values?
As you know, decibel is a logarithm of the ratio of two values.
So, to get absolute value (for example, signal level on headphone output) we need to know reference value.