Q: Are the I2S signals on the MAX9867 chip 3.3Vdc tolerant, or only the I2C ones?
A: The I2S signals are limited by the DVDDIO supply to the MAX9867. The MCLK, LRCLK, BCLK SDOUT, SDIN signals can be up to (DVDDIO + 0.3V). If you are using the EVKit, the DVDDIO is set to 3.3V when JU17 is installed. So you can apply 3.3V I2S signals. If you apply an external DVDDIO lower than 3V, then the I2S signals should not be 3.3V.