There is no config, other than AO6 in the set(s) CLS and a conference key.
For example, make sure Set A and Set B both have AO6 set. Now Set A begins the conference call. Set A calls Set B, C, D, E and F. Set A now has a 6 party conference (AO6)in place. Set B can now conference in Sets G, H, I and J. Now you have a 10 party call. This can go on until you run out of conference resources.
Keep in mind Sets C-J can be on the PBX or external numbers.
Hope this helps,
Scott M.