We also got the Cox email describing the Extended Recording and the On Demand search service..
When we hooked up the "WD My Book AV DVR Expander" (which appears to be the one sold by Motorola) and the DVR gave a message that this service is not supported and to contact your provider.
We also did not have the On Demand search described in the Cox email. After calling Cox Tech Support, a couple reboots and a software refresh and 3 transfers and 30 minutes later because no one new about the service. We finally found someone who took the time to find information and the service will not be available on the 16th so perhaps they push it out all at once tomorrow sometime. When we will tray again.