I first thought my equipment was somehow faulty, because they explain the buttons of this dmx merger in a very strange way. Dmx is like a computer language, it’s not like sounds travelling down the dmx wire, it’s actually a data stream. If you want to combine the dmx signals, of two lighting desks, into one signal, you must set this device to HTP mode, “highest takes priority”, by switching the little dip switches on the back of the unit, please see Thomann’s product photos above, and NOT the instruction manual!. This will then combine two lighting desks signals, into one, single signal, both operating at the same time, with the same channels. The product manual doesn’t show the essential second bank of dip switches on the back of the unit, making the manual incredibly confusing, the product photo shows these though, and don’t set these switches to merge mode either, like I did!, that splits the channels into two separate wedges, for two separate devices, but on one wire?, very confusing. HTP mode, combines both desks together perfectly, right away. Now it’s spot on, very happy, it works great.