AFDS stands for Autopilot Flight Director System. I fly the 757, but I would imagine the 767 is basically the same. The AFDS consists of 3 FCCs (flight control computers, L C and R). Each one can EITHER provide a flight director or control the servos which operate the flight controls, as you say - controlled via the MCP.
Our company SOP is to use the centre autopilot so that the Captain and FO retain their FD information from the L and R FCCs respectively. Once all 3 autopilots are engaged for an autoland the flight directors will disappear.
If, for example, you chose to use the right autopilot, the first officer would have to select an alternate source for their flight director via the appropriate switch.