Active Topics may be limited in Categories using this simple trick.
If you have Active Topics enabled within your Categories, Forums and Subforums, but wish to limit the number of Active Topics displayed in Categories, follow this trick.
1. ACP -> Forums Tab -> Manage Forums.
2. Click the edit cog of a Category.
3. Under "Forum type" click the pull-down menu and change Category to Forum.
4. Scroll down to "Topics per page" and enter the number of Active Topics you would like displayed within the Category.
5. Scroll up to the top and change "Forum type" back to Category.
6. Scroll down again and click "Submit".
Not sure if this trick works with subsilver2 as I do not have it installed on my board. It may not be affected by theme.