DMX + Slave/Master?

master/slave is if you want the 1st gigbar to control the 2nd while in auto or program mode so they go through their programs in sync.

with a DMX controller you are no longer in master or slave mode but DMX mode.

to do what you want, you simply assign the two lights to the same address. you can assign as many lights as you want to the same address and they’ll all be in sync and follow the same commands.