Firstly, I don’t know why this would be moved to the Foundation topic - that is wrong.
Neither stacks are Foundation only and the question does not relate to anything specific to Foundation at all. Child stacks are nothing to do with Foundation, they are a Stacks 3 feature -similarly with HeaderPro, it will work in any theme.
It sounds like that your problem is more related to the Impact foreground content and how to add it. You have two choices:
In the main Impact stack settings there is a checkbox to add foreground content. This will give you a drop zone for content that floats over all slides.
Alternatively, in the Impact Slide stack settings (where your image or video is set up) then there is also a foreground content option. This will enable a drop zone for content that will just be overlaid on that slide.
You can use either or both of these options and drop in whichever stacks you choose as foreground content.
If you want to animate Header Pro text in sync with Impact then you will indeed need to do as @rolisize says and enable the header pro child stacks (button at the top of the settings) and click the blue + button to add an animation effect.