Send multiple AudioTransportSources to some kind of virtual Audio Bus in Standalone App

I try to explain my problem…

I have an app which can play multiple WAV files at the same time.
I managed to be able to send the audio channels of the AudioTransportSources to different hardware outputs with ChannelRemappingAudioSource.

Now I want to insert a step, where I can create some kind of “virtual audio bus”, where I can route (multiple) audio channels to. And in a different part of my app I want to declare, on which hardware output any particular “virtual audio bus” is played.

Do you have any hint for me? How can I get my transport sources to these kind of busses?

Thank you very much.