Hi @camcam
The only I2S functions are on J5, but there is no ModalAI support for it. It has not been on our roadmap, and we only added it in for "Power Users" if they wished to try to develop with it.
You would need to be a trailblazer at this point to try it both in HW and SW, and to enable the alternate functions within the chipset. We have zero experience here so we cannot help at this point. Hence why USB is the preferred approach. If you were on the Qualcomm Developer Network Forum, you might need to directly ask on there for assistance at this time.
Here is the alternate function mapping for both I2S and SLIMBUS if you wished... these pins will be available on our new breakout board in the works (will be a couple more months before we have that ready).
GPIO_142 = I2S_SCK
GPIO_143 = I2S_DATA0
GPIO_144 = I2S_DATA1
GPIO_145 = I2S_WS
GPIO_137 = I2S_MCLK/REF_CLK
Alternatively,
GPIO_142 = SLIMBUS_CLK
GPIO_143 = SLIMBUS_D0
GPIO_144 = SLIMBUS_D1
GPIO_145 = SLIMBUS_D2