Added DVR storage for Motorola DCT6410 III

We got a pre-recorded phone message to our home phone (Orange County, CA) that we can now add a harddrive to the DVR to increase the storage (from the measly 20hrs HD w/160g internal drive).  Message says we can add a hard drive and connect to SATA port of DVR.

I cannot find any information on this on Cox web site or via Google search.  I can  only find information from COX on the Scientific Atlanta 8300 for the Az area and its from 2007.

How do I add storage to the Motorola DCT6410III?