I don't have personal experience with the BGW210, but it has 3x3 2.4 GHz and 4x4 5 GHz Wi-Fi, which is pretty decent. So, you'll first need to decide whether you want to continue using it as your main router. If you do, then you can set up your Orbi as an Access Point to provide expanded Wi-Fi coverage.
If you want your Orbi to take over as the main router, then there is a feature on the BGW210 called IP Passthrough that you will want to enable. This feature bypasses the NAT and routing features on the BGW210 for one designated device, which will be your Orbi.
Note, even with IP Passthrough enabled, the BGW210 will continue to function as a router for all other devices connected to it. If you like, you can use its Wi-Fi exclusively as guest networks and your Orbi Wi-Fi as your main network. Of course, you can also use the guest network on your Orbi if you need coverage throughout your house and simply disable Wi-Fi on the BGW210.
Regardless of how you set things up, keep the DirectTV set-top boxes directly connected to the BGW210. Most IPTV based services use IP Multicast, but many Netgear consumer routers just don't handle IP Multicast very well.
