said by BryanInPHX:"need"... I'm not sure it is really needed, but yes, if you're going to install them install one on each. And don't forget your POE on the tap, if you decide to install MoCA adapters. and a 4th for the cable modem too, for good measure.
why does cox provide them with the TA's if they are only good if you have a moca network or cox's whole home dvr?