Not so much a question, but a finding which might beneficial for others: the Morley PVA (optical volume pedal) can be used as an expression pedal for the Helix.
just connect the expression pedal jack to the output of the Morley using a normal TS-cable.Turn the minumum volume knob to the maximum position.
It looks as if the Helix does an auto calibration (fw 2.53).
For me, the advantage that the Morley has over other expression and volume pedals, is that it uses an optical circuit instead of a potentiometer. So no mechanical wear. BTW: the 9V dc is used only for the the optical circuit, further signal path is passive just like standard expression pedals.