A Sub Out or Bus is very similar to the Studio One Cue Mix in that both provide a copy of the signal and route it somewhere other than the channel specified in the track settings.
The difference is that Cue Mix can use your Presonus Hardware ("Hardware Monitoring") for effects processing, but you'd need to insert an effect into the designated Sub Out/Bus in order for that to work when using "Native" (make your computer do the work) processing.
For more details, Open Studio One, go to the Help Menu, open the Reference Manual and search for "cue mix".
Steven