A “how to install” page with some clear steps rather than digging through a forum post would be nice. Anyway, looks like it needs ‘dtoverlay=audioinjector-wm8731-audio’ which will need a special case in the musicbox scripts. Shame they didn’t do it like everyone else does. If someone is willing to test I will update the image. Or they are welcome to submit a PR.
It’s neat with the hifiberry, justboom and iqaudio boards how the overlay name is basically the product name, so it’s simple to know what overlay is required. But it’s of course not a big deal to map audioinjector to audioinjector-wm8731-audio and I’d forgotten there’s already some mangling going on anyway.
I really like the look of your cards, it’s great to see some innovation.