Sure.

In Simpfony an audio output is assigned at configuration time to a particular zone. What is actually playing to that output is managed by the system, it handles the matrix switching internally. From a setup perspective the audio output assigned to a zone would typically be directly connected to the amplifiers/speakers for that zone, no additional matrix switch is required.

Any audio source may be distributed to any number of zones simultaneously. A line input source is treated like any other source in the system, so there's no limitation on what or how many zones it may be distributed to. Multiple simultaneous instances of the same audio source are support for those that it makes sense for (see below). For example if an installation had 10 zones, the user could play 10 different selections from the same local library at the same time. There's no limit to the number of instances of the same audio source, or the combination of different audio sources in use simultaneously.

Obviously for audio sources such as line inputs it doesn't make sense to have more than one instance for the same input simultaneously (there's only one physical connection per line input). Simpfony understands which audio sources have such limitations and handles them appropriately. Also /some/ online-based services may have licensing limitations which may prevent us from allowing multiple simultaneous streams from the same service/account.

I hope that covers your questions, if not please let me know.