It is possible to compile buildroot however it appears that overlays aren't working ...
Anyone got pointers on using overlays with buildroot and the Pi3/zero W ?
Check the Ultra 2 sound card - use our shop instead of Amazon Europe (Amazon USA is live). Sound card for the Raspberry Pi with inbuilt microphone : www.audioinjector.net Audio Inector Octo multitrack GPIO sound card
Actually it looks like my hardware is not working with the Raspbian build either. I have another Pi Zero W and Audio Injector I will try again on later today.
I only connected one ground from the audio card to my pi so I think that may be in issue. Anyways, I am hell bent on getting buildroot and this all working so I will report back later today or tomorrow on my progress...