Why does only one JR wire need to be fully soldered? So I don’t need all four wires into the DasMikro from the JR cables?
Assuming that the on board regulator is powering your lemonRX then you only need one 5V wire and one GND wire to make a complete circuit as all the GND pins are linked together on the lemon, same thing with its positive voltage pins. So on one of the JR cables you can leave them unsoldered. I would advise that you cut them in such a way that the metal parts of the wires cannot touch.