Soundboard can by event card cast to Sonos speaker, but to Google Home there is no native/event card solution (yet).
Have heard that you can setup a server with desired file, and somehow trigger that url (?) from Soundboard event card, which Google Home responds to - but I am not familiar with this solution (as it is too advanced for me…). Sorry.
You may want to look at this thread:
Soundboard event card «send to Google Home device» is on my wish list…
