But that won't work for new topics as the notification needs the NID which doesn't yet exist.

And using a wildcard: forum/* only confused the subscription settings and returned a blank page with no database update.

I'm using Forum Access and Notifications modules on D6. 

If I'm not mistaken OG Notifications can automatically subscribe group members to all forums/content as a basic feature, but I haven't even managed to get that to work either, and have spent hours trawling through the settings. 

Any pointers or preferred alternative methods greatly appreciated.

TIA