You can mirror a discussion to as many Discussion Pages as you would like, within a section. 

Example
You have 12 pages with one discussion on each page.
Pages 1-4 are specific to Group 1.
Pages 5-8 are specific to Group 2.
Pages 9-12 are specific to Group 3.
You also want all 12 discussions listed on one page.

You can mirror the discussions from pages 1-4 to the main discussion page and to a discussion page titled for Group 1. All three places will give access to the same discussion.
Then mirror pages 5-8 discussions to the main discussion page and a discussion page titled for Group 2, and the same for Group 3. 

You can select more than one Discussion Page when posting a new discussion



By adding more than one Discussion Page in your section/catalog