Asus,
i cant comment on the AC68 but i have an AC66 and regardless of the hardware spec it serves me well, 12 wired clients, 6 wireless running on a 120/12mbps connection, its rock solid and the range is adequate for my whole house
Not sure if this will help anyone, but I was having the same 5ghz issues on my AC66U. I only have the standard 4 channels, whereas i had the higher range too, oh well.
My settings
Wireless Mode : Auto
Bandwidth : 80Mhz
Channel : 44
Any other configuration I used was reverting to...