Set a different name to the 5ghz in the Extreme so you can force the Netgear to join just AC wireless .. it will fall back to 2.4ghz if the performance of 5ghz is poor.. or 2.4ghz is actually faster.. 5ghz still has range issues.. and the extreme is really not going to do any better than most other routers at this.
Since the update to the airport extreme, I cannot see my ac(5ghz) network with my A6200 adapter.
I setup the router again, gave the 5ghz a new name. Connected all other IOS devices. Resetup the A6200 adapter etc...
It only shows my 2.4ghz network.
Running windows 7 with newest driver for Netgear A6200.
Also tried the older driver the adapter came with.