The MAX9768 provides the output (pin 7) and the inverting input (pin 8) of an actual integrated op-amp (with its non-inverting pin at 1.5V). This allows the user to use the op-amp as a preliminary gain/filter stage subject to specifications. Therefore, unity gain is expected for Rf = Rin. Please note that the gain of the second stage is set by the volume control via an analog or I2C signal.
The gain of the first stage can be increased as necessary as long as the 1.8MHz GBW of the op-amp is taken into account and the output of the second gain stage does not swing near the rails to avoid nonlinear distortion.