Do you want to watch the same channel on both TV's or two different channels? The DCX3400 only outputs one channel at a time so, if you want to watch different channels @wees41 is correct ... you will need a minibox or another digital STB.
If you want to watch the same channel on both TV's (or 1 TV at a time), you may be able to split the output. How are you connecting the DCX3400 to your TV, hdmi? Here is an example of an hdmi splitter.