The koala auv3 in-app purchase lets you use koala as an AUv3 plugin. It can have up to 8 outputs.

The effects are only applied to the first output.

how to access your old songs from koala auv3

In order to open older koala songs in the AUv3, you have to open and save the song in koala first. This will convert it to the new format (a .koala file, rather than a folder)

once you’ve done that, you can navigate to the song – it will be in “on my iPhone/koala/songs”

AUv3 and RAM

Please be warned that auv3 plugins have a memory limit of about 360MB (depending on your device), and koala will try to warn you when you’re approaching that, but if you don’t do anything about it, koala may crash. This is not a koala limit, it’s a limit set by iOS.
That said, I’ve noticed that memory limits are a lot higher on more recent iOS devices, the latest iPad Air will handle at least 700MB of samples before it has trouble.