I don’t think this is going to work out. See this manual (https://static1.squarespace.com/static/539f0880e4b0e0318ea3192f/t/5940029fb8a79bde2d979ab5/1497367242457/OX9-Manual-2017.pdf).
It says “When using an expression pedal, the H9 only allows you to have one additional auxiliary footswitch (the left one)”
I was suspecting this but hoping I missed some secret that would let me do what I was after.
Currently on the H9 I can Cycle Up, on the Barn3 I can Cycle Down (Left). So I should be able to use the expression pedal to increase / decrease?