I only have channel aftertouch. I actually don't know which if any off Arturias applications support Poly Pressure. Perhaps Arturia can step in here and tell?
Also in this thread from Presonus Forum
https://forums.presonus.com/viewtopic.php?f=151&t=28857&p=163959#p163959 - Niles who usually is very well into the Studio One stuff write that Studio One does'nt support Poly Pressure. badsearcher claim he has got it to work with an old Modular V or V2 VST2 version. But i have not read it all, and i don't know what works or not regarding Poly Pressure. If it works, then t perhaps require more tracks in S1, and only on MIDI channel 1, as i believe that's how for example a ROLI Keyboard can work in S1.
https://support.roli.com/article/using-the-seaboard-with-studio-one/All of this you perhaps have to find out somehow.
If you find out the above, then i'm interested to know the answer for sure.
Regarding VST2 and 3 versions in S1.
Arturias VST2 and VST3 versions of a plug-in share the same ID. When that's the case then Studio One give VST priority
(EDIT (VST3 priority) EDIT END). Because of this you unfortunately can't have both the VST2 and the VST3 version of plug-ins with shared ID's availble at the same time in S1.
You can either do this before you open S1:
1. Delete the S1 path to your VST3 folder - then none VST3's are loaded but only the installed VST2's.
2. Remove the individual VST3 plug-in from your VST3 folder - then the installed VST2 version of this plug-in is loaded.
Off coarse you can choose to not install VST3's.