The only output selection available is AudioBox ASIO Driver Output Left.  There should be a submenu that allows selections of Left AudioBox ASIO Driver Output, Right AudioBox ASIO Driver Output, and Stereo AudioBox ASIO Driver Output.
 
The audio hardware is Presonus AudioBox iTwo with 2 in and 2 out channels.  All AudioBox ASIO Driver Output channels are available using my Studio One software.  I have uninstalled the AudioBox ASIO drivers and reinstalled them after a reboot, but did not correct the problem.
 
Please help me resolve this issue.
 
 

I assume this is in Track view?
Press the P on your computer keyboard for Preferences.
Under Audio>Devices, check that all your Presonus drivers are selected so that they appear as options in the Track view.

As Greg say Press P to open preferences Select Audio > Devices at the bottom check the box Show Mono Outputs