I am not super well versed on the pixelmad side of things. But here are some recommendations you can check real quick. Make sure you have the right output number and channel assignments selected in the pixelmixes fixture patch sheet. In the DMX Artnet window, universe map tab, this has the mapping from those output numbers to the actual artnet output universes going out. So if you have half of your fixtures assigned to output 0 and the other half on output 1, then the universe map tab should have output 0 and 1 enabled, broadcast artnet 2.255.255.255 (or however the ip addressing of your elc is setup (but should be a 2.x.x.x or a 10.x.x.x), universe 16 and 17. remember Artnet 1:0 is hex.. so that would be universe 16, not 0.

Hopefully that jogs your memory a little bit and you can get it figured out.

You may also want to make sure the ELC has the ability to merge two universes streams like that in a HTP fashion. Never used them myself.

Ryan