Thanks for this thread; it saved me a bunch of hassle! Just wanted to put in my 2 cents:
Using the Dunlop Mini Vol/Exp. plugged into Exp 1/2 jack on HX Stomp with a normal TS (1/4" guitar) cable ie. no splitter, or trs cable.
Step 1 - Open up the back of the Volume Pedal and make sure the dip switches are set to Exp and Ring
Step 2 - In Global Settings on the HX Stomp, set Ring Polarity to Inverted.
This made the Dunlop pedal register as EXP 1 in the HX Stomp. Everything worked fine after that; heel down = 0%, toe down = 100%.