My iOS devices don't see my 5GHz network, my Macs do.

Long story short :

Brand new AirPort Extreme AC Tower (latest gen)

4 iOS devices in the house capable to connect to a 5GHz Network :
- my iPhone 5s (7.1.1)
- my dads iPhone 5s (7.1.2)
- my iPad Air (8.0 beta 3)
- my dads iPad 4th Gen (7.1.2)
(my mom and sister both have iPhone 4's, but they are not capable to connect to 5GHz Networks)

3 Macs :
- My 15" Retina (10.9.4 / 10.10 DP3)
- My dads 13" Retina (10.9.4)
- My sisters 13" Aluminium Macbook (10.9.1)

So, previously we had an AirPort Express (latest gen) and all of the iOS devices could connect to the 5GHz Network; We sold the Express (because upstairs the signal was weak plus AC WiFi is a huge upgrade for me and my dad because our Retina MBPs can handle it) and we bought a AirPort Extreme ; all is good - excellent signal, 1300 Transmit Rate with our MacBooks on the 5GHz Network, awesome speed with our NAS Server - except our iOS devices can't see the 5GHz Network ! If we enter the network name and password in the Settings app the devices can connect to the network but when they scan for networks they can't see it. Plus, after we turn WiFI off, every time we want to connect to the network again we have to enter yet again the network name and password.

What can I do ? I reseted the router and nothing has changed.
Also, It's weird because we are talking about 4 different devices who have different version of iOS.

Thanks

Update : I reseted the Network configs on my 5s and iPad Air ; after that, the devices detected the network and connected to it with no problems but after I turned WiFi off the problem started again - can't see the network anymore. Every time I want to join it I have to go to "Other" and write the Network name.

So much for "It just works", right Tim ?