To go off-show is very easy - you can arrange a tour for 50 euros; splitting it ten ways as we did meant just over an hour of backstage tour with some incredible birds for 5 euros apiece. Bargain! We saw the rearing area, incubator room and some of the breeding areas; unfortunately we weren't able to visit the off-show tropical house where we presume almost all the birds of paradise and the Sickle-billed Vangas are, but you can't have it all.
The giant couas were breeding off-show; we saw a chick in the rearing area. This species was not on show in the park, though the Blue and Crested Couas were. I don't know if anywhere else keeps them.
@olhl.animal.photography As far as I can see, no - but more of the previously off-show areas can now be visited at your leisure so it's a trade-off I guess!