need dedicated access point to use wireless stb?

@Chuckles_2 

You have to use the wap. The wap sets up a private network for the stb and gateway. You can connect the wireless stb to the gateway via cat5/6 cables. Since you are using all the Ethernet ports, buy a 5 or 8 port switch. Keep your stb’s and data devices on a separate wired network though. Data traffic will flood your stb’s and cause your tv service to drop. A managed switch will allow you to connect data and iptv devices to the same switch.  

https://www.bestbuy.com/site/netgear-5-port-10-100-1000-mbps-gigabit-smart-managed-plus-switch-gray/7118008.p?skuId=7118008

https://www.bestbuy.com/site/netgear-5-port-10-100-1000-gigabit-ethernet-unmanaged-switch-blue/6040713.p?skuId=6040713

Thank you for the quick and knowledgeable responses!

I am considering not setting up this unnecessarily complicated 3-device contraption (ap/stb/switch), and instead keeping the current wired STB. I would then make it wireless by adding a IOGear GWU637 wireless adapter. Any advice on whether this is a bad idea?

I have already tested the wired STB with an ethernet cable connection to powerline device, and it works. So the above wifi adapter should work too, but I don't know if any gotchas.

Thanks again,

Since you have used all the ethernet ports already, consider the switch and wap method again. Unless you plan on all wireless devices in the future, you’ll need more wired connections at some point. You are only adding a switch and wap to your setup. Attempting to add the adapter you linked may be more work than plugging in two cables. Just something to consider. You know your home and needs better than me. Good luck with whatever route you take. 

You may want to contact the adapter company and ask if it will work with U-verse iptv (internet tv). 

You do not need to use the WAP.  The wireless receivers can directly associate with your WiFi network.  That is how our wireless receivers are connected.  I too did not like operating yet another wireless AP consuming extra power, an extra port and occupying an extra channel on the already crowed the airwaves.  Our AT&T WAP is neatly stored in a box.

Having said that, the wireless receivers are 5 GHz only so your WiFi network equipment (AP and/or router) needs to have a 5 GHz radio configured with WPS enabled and, importantly, it needs to support IGMP snooping (IGMPv3) and wireless multicast-to-unicast conversion.  Otherwise, you can get the wireless receivers to connect and associate with your network but your WiFi network performance will slow to a crawl and nothing on WiFi will work when your are watching TV.

The IOGear adapter you mentioned will not work well if your WiFi network does not support IGMPv3 or multicast-to-unicast conversion.  If your network supports all that, then you won't need the adapter anyway.  🙂

OK, so that is new information. 5G is not a problem. But our wifi is just what the Uverse 5268 gateway provides; it's got WPS, but no clue on IGMP snooping and multicast-to-unicast. I'd be grateful for some hints on what has to be done.

Will it multicast to 5G clients only, or will 2G clients also be affected? We don't really use 5G much because it doesn't penetrate to all rooms; we could vacate 5G for the STB's use. But I really don't understand this multicast business. Of course Uverse multicasts to all homes, for bandwidth reasons, but within my home, why should the gateway multicast to all wifi clients when there is only one wireless STB? Not that I know anything, but this doesn't make sense to me.

I've run two wired STBs; and the video is not multicast to wifi clients or to other network ports.

Iptv and data traffic is different. The gateway or a managed switch or router with igmp snooping separates that traffic and only sends iptv traffic to the stb. Sending data traffic to your stb floods it with data it cannot read. I would suggest keeping your existing setup. If you just have to have the wireless stb, get it from att and get a switch. A lot simpler than getting a router or the linked adapter and trying to set everything up. Look at the video here to see how to connect a wireless receiver. 
https://forums.att.com/t5/U-verse-TV-Installation/Setting-Up-and-Installing-Your-Equipment/m-p/5061006#M4472

@johnc60: "You do not need to use the WAP. The wireless receivers can directly associate with your WiFi network. That is how our wireless receivers are connected."

I did not find this to be true. Only WPS can be used, and it will not connect via WPS to my regular access point (5268) but it will connect to the provided additional AP.

If there's a trick I'm missing, I would appreciate some clues. It is possible that the firmware has been modified to prevent doing anything nonstandard.

@Chuckles_2 At one point the wireless stb’s could connect without a wap on the 5268 only. When the gateways were updated to band steering, this function was dropped. Thanks to @my thoughts  for this info. 

@johnc60 either has a 5268 that was never updated or has a wireless router connected to the gateway that he has set up to connect the stb’s without the wap. Many people, including myself, use an additional router for WiFi instead of the gateway. 

I should clarify that the wireless receivers will not associate with the AT&T supplied gateway; I have a BGW 210-700.  You will need your own wireless router that is capable of ICMPv3 snooping and wireless multicast-to-unicast conversion.