DMX fixtures don't need to be in slave/master, just set first one to DMX address 001 (or whatever start channel you want to use) then the next one to the number of channels of the previous one and daisy chain the dmx fixtures.
eg
fixture 1 has 11 channels - dmx address 001
fixture 2 has 3 channels - dmx address 012 (1 + 11)
fixture 3 -dmx address 16 (12 + 3)