Nice guess Andrew! But that number is for midi OUT.
I’m looking for a way to set the midi IN channel, which should logically be situated under KeyStep Pro MIDI IN.
Right you are! You know, I was even questioning my response myself, before I sent it. I was actually thinking about the input transformer, like mentioned by TerryM and was thinking perhaps the artist version of Cubase didn't contain this, but I didn't want to risk making things more difficult by saying that, so was hoping it was just something as easy as what I mentioned above, but I was wrong (right?) in the end.
I really hope the artist version does contain the input transformer, or I am not sure how you would be able to work reliably with any of the Arturia controllers, as it is pretty much a must to filter out those channels, to avoid mayhem across your project, by things get triggered, that shouldn't be.