Have a fair amount of code resources for C and pascal for building an artnet external but I just wanted to throw it out there if any of you have already built one and its solid that I would love to buy one. Let me know how deep the bidrectional control and polling is in your external. I am interested even in just a basic DMX in and out setup with no device polling as well. Whatever you got in that udp to DMX protocol header area let me know what it does and how much you want for it.
brandone at brandonepperson dot net