AirPlay problem with the same SSID
I often use AirPlay from my iPhone & iTunes in my PC to play it to my AVR (home theater setup) - Marantz 1506.
The wifi setup in our house are a modem/router from ISP and an Asus RT-N56U (in access point mode) with DIFFERENT SSID's to which I don't have problem playing AirPlay on any device. I needed the same SSID when so I can use wifi roaming without needing to change SSID every time the other signal weakens.
When I set them both (router & AP) with the same SSID, Airplay icon won't show up? But if I set a different SSID from either of the two, airplay icon is back. Channel frequencies are set to ch.1(router) and ch.11(AP). Anyone knows how to set this up?
UPDATE:
Disabling NAT in the access point makes the AirPlay icon always appear but still can't play it through my AVR.
**all are updated**
iTunes 12.4.3
Windows 10 updated as well, firewall off
Marantz 1506 updated firmware
iPhone always updated to latest version
Routers are also updated to its latest firmwares