Is there a way to add a hero image under the primary navigation? It would harmonize the forum with my site better. Thanks.

I think that's related to the theme.

Many themes have sliders that you can configure with a single big slider that could fit your needs for a hero image.

Check the theme sections on the marketplace.

I use magnum theme, but other themes from ipbehero, Brian A & Veilon have sliders too 

Thanks for the help @gabs007