There is nothing wrong with the way you have it connected, but I would make one simple change. I would connect the switch behind the Netgear R6300. The reason why is because when it is connected to the 3801, the routing is being handled by it, and since it is not a gigabit router, your speeds are slowed down.
Also, you want to make sure the 3801 and the R6300 are on different subnets. By default, the 3801 is assigned 192.168.1.254/24.
Finally, if possible, it's always best to have all the U-verse STBs on the same subnet as the 3801. Due to the limited number of ports, that would entail you would need another switch. I actually have one of my STBs on a different subnet, and have had no problems, so this may not be necessary, but we have had a few issues come up when it is not.
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I agree with DavidCS about the additional switch. Having the WAP for the Wireless Receivers on the same RG port as your router doesn't sound like a good plan to me. The RG uses IGMP v3 requests from the STBs to know which ports to send the IPTV multicast traffic to. If you have a Wireless Router on the same segment as the STB (and putting the WAP on that segment amounts to the same things), it will be seeing the IPTV multicast packets.
Some of the newest consumer routers are IPTV multicast aware and handle this; most don't. They end up trying to send the multicast packets on the wireless network. Since the multicast packets have no provision for resending if lost, the router normally slows to a very low rate of tranmission.
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