You use the Mixer window to set up a custom configuration to control various aspects of a tracks playback. Metro supports up to 254 Metro Outputs. Outputs can be assigned to a MIDI or audio port.
Note: Many of the settings in the Mixer window are identical to settings in the Define Outputs dialog box, which you open by double-clicking directly on an Output name in the Instruments Mixer window, or by Option-clicking on an Output Name in the Tracks or Graphic Editor windows. Setting a value in one location sets it in the other.
Instruments Mixer Window Reference