Thanks for the ideas and the input on using ethernet cable and going wireless
But i want to use 3 wire (microphone cable) because it´s durable and the xlr connector i rugged. microphone cable i also very easy and cheap to get.Your are right that its not the wires that is important but in this case it is. the wireless idea will not because the 2.4 Ghz is very crowded already. it also would be needing batteries and some one to turn it on and off and thats is a problem because it is adding error sources.thats why ac on the que light spot is also not an option. all the systems i have seen so far doesn't use a smart micro-controller quelight with the possibility send feedback to the master controller and that works over standard microphone cable.
the quelights needs to be able to connect in a series and in a star network because cables are expensive and running them is time consuming, using one line minimize that. in some situations it is easier to use parts of the network as a star network around a splitter or switch.
I got the idea with the microphone cable from wired intercoms like clearcom or telex. They have duplex audio communication and power on 3 pin microphone cable. in the intercom example one wire has ground, one wire has power and one is for audio. thats why i though that it is possible to have rx and tx on a single cable. I know audio and data is not the same thing but audio cloud be a very slow data rate.
POE mode A is an interesting way to approach this also some kind of phantom power circuit.
more ideas are welcome