Master Table -> Details Table: Different values

Hi, 

hopefully I will be clear enough. Let's image the following tables (it's actually slightly different)

Master Table:

Table_CreateDataSource

Table_AddUsers

Now, what I'd like to achieve is in report to have 2 tables:
`Master Table` and below would be `Details Table`. 

When user selects the activity it would fill the `Details Table` with the details depending on the Activity Name. Eg.  I click the `AddUsersToDataSource` | `99` it would load the data (all columns) from `Table_addUsers` table.

Can someone please guide me on what the DAX would look like. I understand I would have to setup the relationships (plenty of them would be inactive as there will be plenty of other activities... I'm more interested if this is achievable with DAX, that it would return the content of the row with different column names.

Thank you