I'm interested in this matter as well. All I've found so far is I2S for audio output and USB for audio input.
Posts made by Felipe Duque
I2S stopped working on firmware 0.2.2 (b200)
After upgrading the firmware to 0.2.2 (b200), no audio device is listed with either arecord or aplay. I don't recall what my previous version was, but an I2S device used to be shown (both input and output).
I have enabled the I2S pins but still no device is listed.
Anyone facing the same issue? How to proceed?