Hi,
you can activate the additional outputs in the Inspector in the main edit window (I don’t know if there is an option to activate them in the mixer). Just click on the top most Tab that is labeled just like its corresponding track name. Go a little down and find the field where you can choose which instrument to load. Right next to it you find a little arrow to the right in an open box. Click on that to activate all or some of the additional outputs.
