No. Redmi 6A does not have Dolby Digital sound support.
No. Redmi 6A supports 5V / 1A power charging.
Yes, Redmi 6A does have the face unlock.
Yes, Redmi 6A does have the GPS support.
The Redmi 6A is a fairly good update to the Redmi 5A, which itself was barely any different compared to the Redmi 4A. You now get a tall screen, better processor, and improved polish overall.