Resizing the Passthrough Mix Tool
You can use the Number of Mix Panes button to change the display from 4 tracks to 8 tracks. When you select 4 tracks, a button appears that allows you to display the first 4 or last 4 enabled tracks.
With the tool collapsed, you can continue to adjust levels by selecting a track and typing values by using the numeric keypad on the keyboard or by typing a value in the Volume Level display.