A subfixture is a fixture inside a main fixture.
Typically on led bars, you have a mode where you control the whole bar at once and an other mode where you can control each pixel of the bar separately to create some nice effects. Those pixels are subfixtures of the LED bar.
In your case, if we say the wash projector is the main fixture, there is a subfixture to control the laser, one to control the white strobe and one to control the derby effect. Those are subfixtures, and this is why you cannot use this mode with cuety.
If you really want to use the 13ch mode, you will have to create by your self fixtures for each subfixtures. This way each subfixture will be like a whole fixture and there will be no more problems with cuety, just it will use 4 fixture slot in the patch, and you will have to calculate each address of each "fixture".
I hope this will help you,