Share IPTV and Internet on a single cable without killing WiFi?

Hi, everybody.

TLDR; Without getting any extra hardware, how can I set up my network so that IPTV and multicast don't totally destroy my WiFi signal?

This is my first post on SNBForums. I live in Japan. My family and I just moved into a new house, and I'm trying to set up our network so that IPTV works without killing WiFi, and without running any extra cables through the walls.

Here's our setup so far:
- 1 fiber optic modem from NTT
- 1 ASUS RT-AC68U wireless router
- 1 ASUS RP-AC52 wireless range extender
- 2 Netgear GS105 unmanaged switches
- 1 PictureMate 700 IPTV set top box
- 1 PlayStation 3
- 1 Wii U
- Various PCs, smartphones, etc

There are four ethernet jacks throughout the house: in my office, in two of the bedrooms, and in the living room. The IPTV STB and the game consoles are in the living room. Ideally, I'd like the game consoles to be on a wired connection.

I had what I thought was a pretty good setup at first. I connected the WAN port of the router to the modem, I set LAN port 4 of the router to IPTV, and then connected router ports 3 (Internet) and 4 (IPTV) plus the ethernet cable for the living room to one of the Netgear switches so that I could run IPTV and Internet upstairs on a single cable. Upstairs, I had another identical switch, to which the STB and game consoles were all connected. That setup worked fine for wired connections, but WiFi totally died whenever the STB was running or when we would watch streaming video on one of the consoles.

So I decided to run LAN port 4 (IPTV) upstairs directly into the STB and use a wireless range extender for the consoles to get a better signal. WiFi is fine when the STB is running now, but WiFi still craps out when we watch streaming video on the consoles. I have a feeling there's some multicast setting (rate, etc) that I can change to fix this, but I'm not sure.

I'd really appreciate any help you wizards can offer me.

If I am reading this correctly... From your router to the Ethernet drops in your home..
With your configuration, you can only have one Router LAN port connected, to a single switch.

Set up Example: Router LAN port 1 connected to a switch. Plug all your game consoles into that switch.

Router LAN port 2 can connect to a single device, or to a switch in your home for more wired devices.
Router LAN port 3 can connect to a single device or to a switch in your home for more wired devices.
Connect Router LAN port 4 to the Ethernet cable that terminates in the room where the STB is. Connect it directly to the STB.

The RP-AC52 can also be set to AP mode. That would be a much better solution than in extender mode. You lose at least 50 % wireless throughput running extenders.

The RP-AC52 can connect to a switch somewhere in your home, or directly connected to the router, if you don't connect anything to LAN ports 2, or 3, on the Asus router.