Well, I assume that at the beginning I wasn't clear, but concerning to spec I presented them before:
(1) MIC (digital or analog) ->MIC AFE (if analog) ->CODEC-> line driver -------- channel ---------> (2) line receiver->CODEC->DAC ->AMP->Speaker
(1) Speaker <- AMP <- DAC<- CODEC <- line reciever <----------- channel ------------ (2) line driver <- CODEC <- MIC AFE (if analog) <- MIC (digital or analog)
(1) device 1, (2): device 2
Probably one more detail: the channel is not cable, nor twisted pair, but light.