Hopefully you will be working now with XML and HTMLFORMS. My explaination while working on the case was meant to be simple, that you should do what works, and you should do what gives you the best control. I have found that working with populating listbox's that using XML can be best. At the same time I will use a master when it's easier. That is the best advise I can make.
I have sent you an e-mail with a zip file of several examples of chaining. Used in conjunction with the manual, you should be able to create XML and chain the listbox's.
The manual that contains the best information on populating listboxes is the Developing Reporting Applications With Graphical Tools Version 7 Release 6, DN4500798.1208.
Here is a link to the manual.
http://documentation.informationbuilders.com/masterindex/docdetail.asp?docid=1871 On page 271 there is an example on Retrieving Values for Chained Variables With Caching Disabled that provides some XML examples.