Go to the Bus Sends screen of the X32 (select a channel and then press the view button of the BUS SENDS section of the console between EQ and MAIN BUS). You can now edit the mixbus by using the BUS SENDS buttons to choose the mixbus. When on 1-4, the top encoder will control the volume of the mixbus 1. The second encoder from the top will choose mixbus 2. If 1 and 2 are linked, then the top encoder will control volume and the second encoder will control panning. This assignment of the encoders will apply for any linked mixbus. You can verify by watching the screen as you turn the encoder.