On the AudioBox 1818VSL, the headphone outputs share playback streams with Outputs 7 & 8. If you want to create a monitor mix for your headphone output in VSL, you must create a monitor mix for Outputs 7 & 8. Additionally, if you want to hear playback from your DAW or computer through your headphones when not using VSL, you must select Outputs 7 & 8 as your main outputs, rather than Outputs 1 & 2.
NOTE: If you use StudioOne 2.0.5+, and you have the AudioBox driver setup as your audio device, using the template in Studio One for the AudioBox 1818 VSL will automatically set up a cue mix for your sub output 7 & 8. Furthermore if you are using the last driver to support the VSL software, 1.3+ for the AudioBox 1818 VSL, the VSL should set the routing up for you automatically on all your channels and send aux send output to 7 & 8.
PLEASE NOTE: If you are using the latest driver for the AudioBox family, Universal Control 2.1, you'll notice the VSL software has been removed as it is no longer supported.
You'll need to configure your DAW to use outputs 7/8 in order to use headphones. If you are also using studio monitors you can move their cables from the main output -> outputs 7/8 on the back of the 1818. This is if you are using the latest driver for the AudioBox family, Universal Control 2.1, you'll notice the VSL software has been removed as it is no longer supported. will ensure you hear your audio from your headphones as well as from your studio monitors.
A video explaining the set up for head phone output using the VSL software: