We can try.
Have you read about Control Link in Presonus manual, and have you mapped your Hardware controller like guided in the manual?
Else do that.
In this video you can see something about mapping your contrlloer globaly for control link in studio one and other things. Can't recall.
It's for Studio One 2, so only functions for that is included. But the global mapping and other things is still used.https://www.youtube.com/watch?v=hjX5zjJv4Y8
I can suggest you try to load a track with a multiinstrument. You find Some in Studio Ones browser.
When this is loaded you see that 8 parameters is already set up for the 8 visible knobs.When you have mapped your controller for Control Link and assigned it to this macro controls, then you can use your hardware controller to control them.
Over the first knob you see 3 symbols. At the left one for the view you are in, at the right one for the structure set up of the multiinstrument, and in the middle a wrench for going to the parameter set-up window.
In the parameter window you can add many parameters for a single control. You can also select a way for a control to behave under Trans.
Over the virtual keyboard you can see what instruments there are in the multiinstrument. If you click on on of the lines the instrument open, so you can modify the sound.
In the first view where you see the control knobs you can click the arrow just under the buttons and open for Control Links X/Y controls.
Drag Modular V to a track of it's own.
If you for instance on the left of the track click on the number for the track or click on the symbol just under the recording in the mixer channel for your Modular, then a window open that have the same controls as mentioned above.
If you click on the wrench over the first knob you open the parameter window. In there you find all the parameters for the Modular just like in the multiinstrument.
You can now for instance select knob 1 and add for instance width 1-3 for that knob. You can even select differnt modes under how the knob shall effect witdh 1, 2 and 3 under Trans. (You could also control both LFO 1 and LFO 2 on SEM with one knob and even reverse the polarity for one of them.)
When you have mapped you hardware Controller for Control Link and then activate this knob and then move a mapped control on you harware controler, then you'll see the contol link macro control and you harware control in the control link display , and then you can link them together by pressing the link arrow between those in the display.
(You can see the Control link display on the top left of Studio One or make it visible in the active window by clicking the technical symbol at the top right of the open control window next to the active controller drop down menu. Also be sure you have selected the mapped controller you wan't to use in that drop down menu.)
This is one way to do it. Allways eksperiment and read more about it. You can do things more ways than one.
If you wan't to you can now drag another plug-in to the same track and combine the instruments. Now this instruments parameters is availble in the parameter window too. And you'll be able to control More synths parameters at a time using the same hardware control knob. Just add the parameters in the parameter window as explained in the first example.
____It's important to know that you can only control the control surface you have open.
So if you wan't to control parameters on two synth at the same time, then you'll need to combine the instrument - use a multinstrument.
So you can for instance link a parameter from one synths own GUI on one track and another parameter from another synths own GUI on another track to the same hardware control using the "normal" Control link displays arrow tool. Then your control are on both parameters, but you will only be able to control one synth at a time.
And linking this way not using the macro controls you can't add more than one parameteron a synth for a single hardware control, Perhaps that's what you was told on the Studio One forum.
To add more parameters in the same synths for a single hardware control you need to use the Control Link macro controls and assign parameters likr explained in the examples above.
INFO: You cam also create FX links for FX using splitter and so on like you can for instruments in multiinstruments. But that's another thing you can research.
If you need a more step by step guiding, then please start creating a example and then ask me what to do from there. Perhaps you only wan't one step at a time.