So here is what I know, Isadora is capable of sending 4 Universes of ArtNet per Device, so if you have a device that is capable of sending more then 4 universes you can't use it in Isadora 3 (It is capped at 4), or atleast that was the case in Isadora 2.6.x. Don't know or Isadora 3 changed that.
2x DMXking LEDMX4Pro's should be capable of doing 8 universes, more then that and you need more DMXKing to work around the cap.
Can you tell us a bit more about the behavoir "funky" ?