If I have 4 channels ( 2 Tx & 2 Rx), how many I2S ports would I need to interface the part?
Assuming they are both on the same clock domain and same sample rate, then only one. One set of clocks and then the input data and the output data.
If they are not both clocked from the same master clock, since you are using the terms Tc and Rx I might assume the data is over radio or Ethernet or something? In that case they are on different clocks so you would have to use two ports for the two clock domains. One will be for Rx and one serial port would be for Tx.