Re.: Recommendation about passive CM filter at input of the differential amplifier, a couple of points to consider.
1. At DC the resistors of the CM filter change gain of the following differential amplifier. This is easy to compensate by using smaller value resistors at input of the differential amplifier.
2. At AC the effect of the CM capacitors tolerances can be big, simulation can show this: the differential voltage that comes to the DA is affected by the capacitors and their tolerances.
