Lately, I've been working on the proto board of a cs42448 codec, which would allow us to have 6 audio inputs and 8 audio outputs. It's a very convenient and cool chip, but as I understand, it has been discontinued, although it can still be purchased in some places.
I designed a board for our stacking prototype and wrote a basic code to configure it through I2C. I set up the SAI in TDM mode for STM32, but so far, I haven't been able to hear any sound.
I feel that it might be worth exploring other more popular solutions, even if they involve a more complex connection to STM32 (something like three SAI simultaneously (or 2 SAI + 2 I2S channels), but that would only give us 6 channels on output, and we would like 8 channels to have a separate stereo channel for headphones). As I mentioned earlier, most likely, for headphones, I'll use a simple stereo SPI DAC, possibly with a built-in amplifier.