Mike,
To operate DCS and TMCC on the same layout, you only need an MTH #50-1001 DCS Remote Control Set (http://www.mthtrains.com/content/50-1001) and a Lionel TMCC command base and Cab-1, or Legacy command base and Cab-2.
Using this setup, you would operate your MTH DCS engines (PS2 and PS3) from the DCS Remote and TMCC engines from the Cab-1 or Cab-2.
Alternatively, you could run both DCS and TMCC engines from the DCS Remote. In this case, you would need only the command base and, instead of the Cab-1 or Cab-2, you would need MTH cable #50-1032 TIU/TMCC-Legacy 6' Connector Cable (http://www.mthtrains.com/content/50-1032.
This and a whole lot more is all in "The DCS O Gauge Companion 2nd Edition", now available for purchase as an eBook or a printed book from MTH's web store site! Click on the link below to go to MTH's web page for the book!