The electrical specs do not provide any idications as to what the input impedances are for both Main and Aux A/Ds when they are using PGA/Buffer, or when the bupasses are activated.
Can this be spec'd?
Input resistance? Input currents? Dependence of input current on the input voltage? For various situations -- with and without PGA/Buffer..
The input structure of the A/Ds must be some form of a switched-capacitor arrangement, so it will probably behave as a pure resistor (for signal frequencies) -- for the unbufferred operations.
(A separate discussion reveals that, for example, the Reference inputs, in a specific configuration (unbufferred, of coarse), may require 3 uA of current.)