I wouldn't advise the youtube videos as if they can hear something close to them but can't see it they get really distressed. At least that's my experience with other birds

I think when the baby arrives and the Sennie can see the huge pink unfeathered being with no wings and too many feet

he'll understand where the sound is coming from. When your baby arrives I would advise perhaps moving the bird to a quieter but still social area where you can still sit with the bird, when the baby is sleeping perhaps?
The bird will need the same amount of attention as it did before the baby but I'm sure you know that. Perhaps a slight relocation of the cage might be better?
Perhaps an actual Sennie owner could help you a little more.