ATT Uverse

For the least amount of grief, you should always keep the UVerse DVRs connected to the UVerse gateway.  All other, regular devices can use the Orbi.  There are two ways you can set up the Orbi.

1. As an Access Point.  Your UVerse gateway continues to function as the main router for your entire household.  This is the easiest method to set up.
2. As a router, in case you want to take advantage of features on the Orbi that the Uverse gateway lacks.  The UVerse gateway has a pseudo-bridge mode setting called IP Passthrough or DMZPlus, depending on the model.  The gateway bypasses NAT for traffic that it sends to the Orbi, thereby avoiding the double NAT problem, but the gateway continues to function as a router for all other devices directly connected to it (i.e. the DVRs).  This is one of those rare situations where having two routers in a household is ok.  This requires a little more effort to set up, but there are reasonably good instructions on the Internet that you can follow.  These are pretty good.  
   
   Note: The Orbi's firewall will block the DVRs from accessing anything connected to the Orbi.  I canceled UVerse TV a long, long time ago, so I don't know if their DVRs have any local media streaming or DLNA-type features, but they won't work.  Something to keep in mind.