Usually when I see a question like this it may involve an audio device which has it's own software mixer. From Studio One, the Main stereo output will pass through said software mixer for the audio device in use. This could be an Audiobox, Firestudio, Studiolive mixer, Studio 192 device, etc. So you will want to look in the software mixer for your device for the stereo audio stream coming from Studio One. Usually it will appear as two mono channels that are NOT panned. You will have to stereo link or just pan the first stream hard left and the second stream hard right to hear the stereo spread coming from Studio One.
Please refer to the manual for the audio device you are using for further help and detail on how to do this. You may also wish to put in a support ticket with more details on what you are doing and what you are using for better help.
