Yet another board begins with discontinued but extremely overspeced components. The AK4524 came from a 17 year old Terratec EWS 88, a $600 sound card which no longer works on any modern computer. The lion kingdom used 6 of its 8 channels exactly once, to watch Gladiator in 6 channel sound. It was later used as a 48khz oscilloscope.
The AK4524 is no longer sold, but the I/O is similar to any replacement. The AD8604 is the 8Mhz rail to rail op amp from the day job. All the STM32 does is convert I2S to SPI.
It has a temporary power supply, with plans for mounting directly on a raspberry pi. The mane problem is the through hole crystal keeping it from laying flat.
What is the point, when a tiny soundcard for a raspberry pi is virtually free? It's about getting better sound quality from the headset microphone.
The very best ADC is the PCM4222: 124dB, 2 channel, 216khz, 24 bits with differential inputs. The very best DAC is the PCM5242: 114dB, 2 channel, 32 bit, 384khz. They're equivalent to the very best analog tape decks ever made. It might not not worth reusing the remaneing AK4524's for anything beyond recording a headset.