Having searched, it would appear that the MTH WIU has pretty much vanished in availability. There are a few possibilities on eBay - usually running over $500 each; for a product that had a retail of about $160 to start with - that's WAY off of the charts.
More importantly, if you are using a generic wireless router - which are available for $40 +/-, it would seem that ALL that is happening with the WIU, is that it is taking that inbound signal via the wireless router, via an ethernet cable, into the WIU box, and then sending that signal via a USB (serial cable) to the TIU. eBay, and other places, have PCB's with ethernet to serial conversions for $15. Does anyone have any knowledge of any of the smarts that go into this??