Cant help with the ESS as I'm on parallel port here, no as long as you can jog the Z with the PgUp / PgDn keys on the keyboard there is no output to set.
Have you got an "Arc-Ok" signal? If yes then the "Allow THC when not in THC mode" should be unchecked I think.
Do you have a value in the THC rate DRO on the settings tab? Try 20% to start with.
You could try going into ports and pins, inputs, and flipping on "Emulated" for THC-Up & THC-Down, just for a test, this should allow you to kick the z up/down with the keyboard by pressing U & D respectively, may have to set that 'allow thc when not in thc mode' back to on to do this but put it all back afterwards.