I think Jackal may have answered you with the links but yes you do more or less as you said. The power for the motors/drives will need to come from a power supply that you have to provide. As you already have one for the original amps (drives) then it should be fine, just double check the voltage of it before you hook it to the drives but if I recall it should be well within the voltage the Dugongs can accept.
As fior Jackals question about the xml, if you are supplied an xml then its just a case of pasting or dropping into the main Mach3 folder, you can then use the Mach3 Loader icon to start Mach and then in the list you will see the name of the xml you just copied to the folder, click on that and it will start that profile.
Hood