First check whether the Enable signal is working properly. When you power up the Duet, the motors should be un-powered and therefore free to move. When you try to home them, or to jog them (with M564 H0 in config.g or sent first to allow movement before homing), they should be powered up and no longer be free to move. If you find they are locked to start with and become free when you try to move them, then change R1 to R0 in your M569 commands for the external drivers.