According to post 19 of the thread
Would it be possible to create an Optical Out?, the information transfered through I2S is the master clock, the bit clock, the data, and the left and right clock. The WM8975's pin 1 is the master clock, pin 5 is the bit clock, pin 6 is the audio data, and pin 7 is the left/right clock. If you can somehow find the traces leading from these pins, I think that
it's at least possible to get an I2S signal from the WM8975. But let's also remember that possible isn't probable.
Now I just want to see someone pull it off
