Use a GD theme within a WP Theme

I have a newspaper site that uses the Newspaper 6 theme which is wonderful for the newspaper section. We are using Geo Directory for the for our business directory, events, and some CPT. We would like to use the Newspaper 6 theme for all of the newspaper sections but then use the Geo Directory Modern theme for all of the Geo Directory pages.

Can this be done through pasting the Modern Theme css into the Geo Directory Pages or the theme capatibility settings? I know there has to be a way to do this, but what is the easiest path?

Thank you for your time.