Recently we encountered problems when we tried to directly control DL.3 fixtures from DP8000 ArtNet output. It seams that DL.3 fixtures requires ArtPollReply packets to be sent from Art-Net sources to receive Art-Net ArtDmx packets.
Anyway, I think DP8000 should respond to ArtPoll packets to identify itself to conform with Art-Net specification. To fully achieve this, every 4 universes should have its own IP address (limitation of ArtPoll reply packet).