The REV. L TIU is the best option here. The REV. L has both a USB port (for connecting the WIU) and DB9 serial port (for connecting the TMCC Base).
You can use older versions of the TIU (without the USB port) but you will need a splitter for the DB9 port for both connections. You will also need a USB to Serial adaptor for the WIU to plug into the splitter.
The new WTIU coming out this month already has the WIU built in so all you'll need is a USB to Serial adaptor and the TMCC to TIU cable to make the connection. The WTIU is primarily designed for use with the MTH app and the DCS handheld remote can only be used in a tethered mode.