I would remove the aril completely, that's the part the toucans are after. Leave the hard seedcoat though. I think it survives the trek through the bird's intestinal system.
I'm sure parrots and other birds can destroy the seeds altogether before eating them but toucans with their oversize bills aren't equppied to do anything but eat them whole.
You could try removing the hard seedcoat and then treat with GBA just as an experiment.
I imagine you could dilute the muriatic acid maybe by about half and soak for five or ten minutes then rinse thoroughly. Hopefully it inactives any germination inhibitors, but treating with GBA might be a good thing too. This of course would be with the seedcoat still on. I wouldn't treat the naked seeds that way.
Sounds like you have a lot of seeds to treat lots of different ways.
As a broad guess I would think that the surface of the soil is covered with litter like you described earlier but underneath I would suspect laterite clay. Most rainforest areas have very little topsoil since the nutrients get sucked up into the canopy very quickly. (This is why tropical soils are so poor for grazing cattle, the soil doesn't really carry the nutrients, they're all up in the canopy.)
That said most plants are pretty adaptable to their soil needs so I wouldn't worry about it too much except perhaps to make sure there is lots of iron available. Laterite is very rich in iron and I have grown a few tropicals that are prone to iron deficiency if not grown in high-iron soil.