Wayne,
You don't need anything else to operate your conventional engines.
Just connect the output of the left handle of the Z4000 to both the Fixed #1 and Variable #1 channel inputs on the TIU, red terminal to red terminal and black to black.
Next, connect the Variable #1 channel output to the track, red post to center rail and black post to an outside rail.
Place one conventional engine (start with the Locosound engine, #30-4088-0) on the rails, turn on power from the left handle of the Z4000 (all the way up!) and turn on the DCS Remote.
Press TR on the DCS Remote, highlight Variable #1 in the remote's window and press the thumbwheel.
Scroll up voltage from 0 to 6 volts or so. The Locosound engine should start up.
Now, use the buttons on the DCS Remote as if they were on the Z4000, and use the thumbwheel as a throttle, to operate the engine conventionally.