Click the 
icon on the toolbar.
This will open the Output Configuration
dialog box.
On the left-hand side of the Output configuration dialog box are the Cue chan: sliders.
Adjust the Mix slider to alter the ON-AIR output level in the cue channel.
Adjust the Out slider to alter the CUE output level in the cue channel.
Tip: If you are trying to connect headphones directly into your soundcard output channels you will most probably find there is not enough level to drive your headphones. You will need to amplify this signal up to headphone level. You can purchase small amplification units for this purpose from an electronics store.
Note: Cue channel support is not available in all OtsAV versions. Consult the OtsAV.com web site for more information.
How to optimize Air & Cue cross talk
Output Configuration dialog box
How to set up your soundcard (main channel)