Easy to do….think of the FX returns just like any other input channel.
Select your live stream mix, that puts all the faders into sends on fader mode, then
go to the FX returns, they will also be in the sends on fader mode, just bring up the faders to the level you want the FX to be on the live stream mix.
Check that the FX return is assigned to the streaming mix and that it is in post fade, I assume all the channels are set post fade for the live stream mix.