I do not own a Zynthian, but I remember that exists a page in webconf for manually changes the audio interface configuration.
My idea is something like a checkbox/select/dropdown box for the user select your audio interface. Also, if the user finds it necessary, you can change some of the default parameters loaded in the select.
The default configurations could be in a repository only for this purpose, so that it would be easy for people to suggest default settings for new audio interfaces.
Webconf could load them directly from the internet, always getting the newest integrations with audio interfaces. Another possibility would be to make new configurations available from webconf updates.