I couldn't find this information so I am posting solution here. I wanted to use Zoom R16 as a control surface in Studio One 4 but wasn't able to find any reliable information about using it in S1 - although I came across many folk in forums who had tried and failed - as had I when I tried to connect it as a Mackie device (or anything else), or use the midi learn functions.
However I came across a youtube video of somebody using his Zoom R16 to control transport in what looked like Studio One...so I went back to it - this time I ***upgraded the firmware*** on my (quite old) R16 before trying again with S1. Now seems to give me zero latency option now in S1 which I don't think showed before. Also now works well as control surface - set as external device: Studio One - Options - Add External Device - Mackie 'Control' (change name if wish) Receive and Send From Zoom R16-24 and full transport and (non-motorised) fader control can also be yours. Also seems happy to run as a control using another soundcard as audio processor.
Hopefully this might work or help somebody else out too.