Well, just to try to be of help, I'm going to try to answer, but I am no expert, and a very recent Sonar refugee. I was trying to do the same thing you are. It appears that the volume and pan only work with audio tracks. in the midi controllers section of studio one, there is no Volume (#7). I went to Presence XT and right-clicked on the volume knob and got volume automation options (which shows up as "something" Gain as an automation in Studio One, sorry I am at work and I can't remember exactly what it said. I selected the second option from the right click on the volume knob and was able to automate the volume of the instrument.
I hope that helps and is not too confusing. I can do it again when I get home and step you through it if that will help.