it took my brain a moment to reason out why this creates an offset, rather than actually changing the gain.
a naive conclusion would be that the DAC changes the gain, because the voltage divider created by the resistors is simply creating an input voltage, and the DAC can push that voltage around.
however, a second glance reveals that the voltage divider is not creating a fixed voltage, it follows the AC signal. since the DAC just offsets by a fixed amount, and does not follow the AC signal, it cannot be modifying the gain, only creating an offset.
do I have that right?