Transceivers can both receive and provide audio, and streams can be routed from one node to any other, including many others. The tricky bit is how to expose the audio routing in DT in a sane way. The way it is implemented here, the slave nodes specify the number of slots they each consume and generate, and which thereof they forward from one side to the other. This mimics the internal register structure and should allow for even exotic setups.
It was my understanding that the A2B bus is bidirectional but with separate time windows allocated for host->device and device->host transmission. The wording seems to hint at device-to-device communication but I wonder if this is really what you meant.
