If you are needing to separately "mix" the signal for streaming, you will need to use one of the aux outputs. This will allow you to mix the faders in the Aux output you selected. If you want to send the FOH signal (already mixed) out for streaming, assign all the channels to one of the sub-groups and use that sub-group output for the stream. Also, you can use one of the "Main outputs" for the mono stream, assuming all the inputs are not panned (for stereo).