Hey mate,
Rather than running over Artnet directly, you can use the Artnet second universe and convert to DMX using a cheap artnet note, such as this:
https://www.chauvetdj.com/products/dmx-an/
That way, you still have 2 universes off the one D512 interface: one off your interface, and one off Artnet. The Rezotubes can simply plug in via DMX, which would adapt to Artnet via the interface I linked above.
Hope that helps!