A dual opamp U1 is used to shift both REFGND and REF by (DUTGND + 300-mV offset). Table 24 provides the nodal analysis of the circuit. As evident, the DAC outputs track the DUTGND with an offset of 300mV. This offset can be easily compensated in software. Note that the absolute ...
It looks like it has to traverse the whole circuit board (from edge to middle) without any buffering... this would make it extremely susceptible to both digital signals and audio crosstalk.Additionally the headphone out can feed a relatively low impedance, so this could cause voltage noise ...