Nope, you will define the pixelnet universe to channel 1. Since you are using single USB dongle configured for pixelnet for all output, all of the channels need to be defined to that device which in this case is a single pixelnet universe. The active hub pulls the first 512 channels of this pixelnet universe and converts that to DMX. It also sends those same channels out on the pixelnet output ports so no pixelnet channels are lost, only duplicated. As long as your device start channels are defined correctly, the controllers will work as expected and from what I can see in your description, they appear to be.