Hi,
I am assuming that you will connect them to one of the 4 pixlite 16 dmx outputs?
If yes, then nothing special in xlights. What are you driving off them ?
Let's say that the first 3 channels are dumb lights,mthe u define a model xxx, and set the start channel to the channel of the 27 controller. So I'f u set the 27 to start at 50 ,then model xxx would start at 50. I'd u then had a face with 9 channels, the model channel would start at 52 and u would connect this to the 2nd block output of the 27ch etc
The dip switch of the 27 channel is used to set the start address and then it continues from there.
I have two of these for singing faces, dumb lights etc etc