Help: Grandstream GWN7610s

I've picked up a couple of these and currently playing around with them and I for the life of me can't get any devices to connect over 5ghz

All wireless devices in the house are connecting on wireless N over 2.4

Things I've tried are

upgrading the the latest firmware - v1.0.5.15

creating a secondary SSID with the option of 5.0 only and have enabled it but I cant see it broadcasting - it pops up everynow and then but whenever I try and connect to it keeps returning a invalid password message

changing the priority of 5.0 to highest

changing the primary SSID from dual-banding to 5.0 - This resulted in not being able to see the SSID broadcast at all

I have two of them so to rule out a faulty AP i've tried using them one powered up at a time with the same results

The throughput on these have been quite lack luster but I'm putting that down to the over saturated 2.4 frequency ?

Thoughts anyone?