The AD777x family provides a PGA per channel which can be independently configured.
The PGA is a capacitive programmable gain amplifier offers a good performance, including high common-mode voltage rejection, low noise at low frequencies, low offset, and low offset drift.
This PGA makes unnecessary the used of external buffers.
More information related to PGAs: Integrated Capacitive PGAs in ADCs: Redefining Performance | Analog Devices