Hmmm.... had a family member with an RT-AC3200... here's what we did to get things sorted...
1) Break apart the 5G radios with Standard Setup (e.g. no more Tri-Band Smart Connect stuff)
5G-1 became "WirelessMedia" SSID
5G-2 became "Wireless"
2) Went common SSID with the 2.4GHz radio with 5G-2
2G - became "Wireless" as the SSID there
3) He wanted a Guest Network, so we enabled Guest on the 2.4GHz radio only... as "WirelessGuest"
For the rest - set 2.4G as B/G/N (disabling Turbo), and Mixed/Auto for the 5G radios..
Client side - streamers/STB's all got "WirelessMedia", the other clients got "Wireless", and of course, guests get "WirelessGuest"