In DMX, you can have multiple devices responding to the same channel. Since you can program each servo or LED's channel individually, just set the unused ones to one of the channels you are using. They will do the same thing, but since there is nothing connected to them, it doesn't matter. So on board 1, the servos would be on DMX channels 1,2,3,1,1,1,1,1 and on board 2, 4,5,6,4,4,4,4. Or even beter, 1,2,3,1,2,3,1,2 so if something happened to one output, you could just move the cable over without reconfiguring everything.
This would even work for devices where you can only set the start address. If you have an LE starting at channel 1, and another at 5, and only use the first 4 outputs of the first one, there would be no gaps in your channels, however, the remaining 12 outputs of the first LE would be the same as the first 12 of the second.
As for channel 0, there is no such critter in DMX; channels start at 1.
/mike
