If I understand you want some members access to your private forums. There are more simple in my opinion, you edit your private forums by adding members that you want and then protect a member names and password and enter a password in the space provided<
Cordially, Maxime
Taxation consists in so plucking the goose to get the most out of feathers with the least possible cries.(Jean-Baptiste Colbert)
The User Groups mod will do what you want. You can create a group which has access to any/all private forums, then simply assign someone to that group and the task is done.<