[support] Organic Groups - Moderating Group Owner/Group Subscriber Roles

I am using Organic Groups with Drupal 6. Any group can be created by authenticated users.

How do you promote a group creator to "group owner" role, and how do you promote somebody who joins a group to "group subscriber" role (where they can post to groups).

The fundamental difference between a "group owner" and a "group subscriber" role is that a group owners can edit/delete posts within his group (and possibly change workflow) - and I want this distinction maintained.

Which module would most effectively achieve this?

(I have tried Organic Groups User Roles module, but that doesn't seem to do the trick in a simple and effective manner.)

Thanks for your help.