Harmy said:

Well, apparently, Encore doesn't support adding more than 8 audio tracks, so I'm gonna have to use something else to author the BD - I think I'll try MultiAVCHD but I find it a bit confusing.

I'm still sticking to Encore for the Blu-ray, but on the other hand we're filling the disc to the brim with bonus material, so there's no room left for more audio tracks anyway.

Still, IF you find a decent way to create both custom disc and pop-up menus in MultiAVCHD, be sure to let us know.