Hi Kaoru - thanks for the response.
When the checkbox from List B is checked in the form, I am setting the multi selection listbox to equal that List B item ID that was just checked.
The multi selection listbox has a separate data connection to list B as well. It has a value of each list B item ID, and a display value of the item title.
What I'm looking to do is have a "query" data connection where the user can search for multiple items in List B, and then select the items they want to include in the current form.
The items that have been included in the current form from list B should be stored in a format where later on I can re-query them to get more detail about them from list B.
I don't know how to re-create this since I'm using a lookup in the form and the SharePoint server is secured.
I am using a SharePoint list right now, however, if needed, I can use a Form Library.
I've included screenshots to try to help.
Hopefully this provides a little bit of clarity...
Let me know if it's still not making sense.