Geoff,

You need to go to the Mach website at Machsupport.com and under downloads, Plugins select the file for the shuttle pro, very near the bottom.
This file does all the shuttle devices.

Install that file into C:\Mach3

Then open Mach, go to Config > Config Plugins [ 4th from bottom ] and tick the shuttle plugin to enable it.

Then click config and you get a picture of the shutle pro and a choice of boxes to fill in.

You have ordered the Express so click that, bottom right and just use the inner top row of buttons and the two wheels.