when i worked with DMX (only once and not with an enttec) it was crucial to plug in the device after the system had booted. else it would just freeze (no matter how i tried to blacklist and/or remove offending modules)
while it was ugly, it was acceptable as in this special case it was guaranteed that the machine never had to reboot without human watchmen....
i actually have to plug it in twice :-) otherwise it would not attach to /dev/ttyUSB0
erich