In order for you to set up the Sound Active Mode via Master/Slave, or Primary/Secondary Mode, you will need to do the following:
1) Set up your Primary light, Master, to Sound Active Mode.
2) Connect a DMX Cable between the Primary and Secondary unit, the Slave, by going DMX Out of the Primary light and DMX In to the Secondary light.
3) Set your Secondary light to the DMX Mode setting, which should read "d.001".
Let me know if this helps.