i cannot find the info on how to use lionels tpc units with the dcs system.
what page is it on in barrys book?
That's because it's unnecessary for DCS and therefore it's not discussed. There is, however, a reference to "devices that can combine the output of two or more transformers into a single power feed" on page 117 of the 2nd edition:
As discussed, the only real advantage gained by wiring for Passive TIU mode of operation is that track power may exceed 12 amps per channel without any concern of damage to the TIU. This would allow use of higher capacity toy train transformers or devices that can combine the output of two or more transformers into a single power feed.