Hi @QuBiQuiQ,
Thank you for your message.
Audio Unit comes with separate limitations, which we’ve tried best to summarise in our dedicated Limitations of Audio Unit article.
Several years ago Apple introduced Audio Unit support for iOS, which provides much more flexibility and can be seen as their successor of Inter-App Audio (which no longer is maintained by Apple).
Firstly I’d suggest to get in touch with the 3rd party app vendors, to ask them about their plans to release AU versions of their plug-ins. Alongside, it might make sense to browse the app market for AU compatible guitar effect plug-ins.
In regards to register Cubasis, please open the in-app shop and follow the steps to unlock the free RoomWorks SE reverb plug-in , which works via registering the app.
Hope that helps!
Best wishes
& stay well,
Lars