Use case for i2s slave mode operation;
Ability to interface with an audio system that can function independently of the host board, for instance;
Si4743 (slave) + CS4360 (slave) + PCM1862 (master)
PCM1862 is a multi-channel (8 channel, 4xstereo) ADC + digital MUX.
Si4743 is an AM/FM/RDS receiver with analog and digital (i2s) output.
CS4360 is a multi-channel (6 channel, 3xstereo) DAC with independent volume controls (i.e. duplicate stereo signal across three pairs FL, FR, RL, RR, center, sub).
*all controlled via i2c.
Put that all together, and you have something that can be set for AM/FM playback while the host board is OFF, but only if you can keep those i2s lines operational. But more than that, the PCM1862 obviously needs to receive i2s from the SBC, and could even transmit TO the SBC. I.e., microphone attached to the PCM1862 sending audio back to SBC for recording/call/etc.