I notice that there are no longer any monophonic instruments in GPO4. Not by default anyway - the Auto Legato feature does seem to include this functionality. However, as solo instruments are usually the most expressive and most exposed, it clearly seems necessary that a solo instrument be playable with manual legato. Is there a hidden controller for this? Perhaps something in SONAR? Or am I stuck with editing each note in the piano roll to avoid overlaps?
The initial version of GPO4 does not allow the user to adjust polyphony unless an adventurous user wishes to explore sfz file editing. GUI adjustability is planned for a future update. Until then, you will indeed need to edit for minimal overlaps to get the most convincing results with cc64 legato. The present (essentially unrestricted) instrument polyphony is a necessary default compromise to allow consistent performance for auto-legato and other requirements like Akai EWI compatibility.