I2S - Ribbon Cable - Termination
For a point to point link like this there is no reason not to go for source termination, 100 ohms more or less, in series at the driving end of the cable as close to the processor pin as you can get it. 

It terminates the energy reflected from the load without increasing the drive requirement, but you should allow for the impedance of the source pin (hence 100 ohms give or take rather then 120 ish).

Where is your MCLK source, that is the one that really matters for system performance as it is what drives the modulator?