I think you did not understand my explanation above. Go to the screen where you create or edit a topic in the back end. On the right column you’ll see the small metaboxes where you specify the forum, etc. Above that you’ll find a box with a single checkbox saying ‘Send Notifications’. Make sure it’s unchecked when you click Publish or Update and no emails will be sent out.
If the checkbox is always checked when you load the screen, it’s because the option to make it always checked is set in the bbpnns settings. Unset that there and the checkbox will no longer be checked when you create a new topic or reply.