BGW210-700 router (AT&T) and EX6100 AC750 extender connection issues

Has anyone tried to connect the EX6100 AC 750 extender to AT&T's Arris BGW210-700 router?  When I log into the BGW210, it shows both the 2.4 and 5GHz frequencies enabled and I know that it connects to devices with whichever frequency gives the strongest connection.  With this said, while setting up the extender and selecting the current networks to extend, the extender can see the 2.4 GHz network, but the 5 GHZ doesn't show up as an option to extend.  I tried manually adding it and it can't connect.  Even when the extender is moved much closer to the router, the 5 GHz network still doesn't show up.  Is there a setting on the BGW 210 that needs to be changed to make the 2.4 GHz and 5 GHz networks show up separately?  I was thinking about getting a more robust Nighthawk extender, with tri-band technology, which would dedicate one 5 GHz band to connecting to the router, but if I can't locate the 5 GHz network from my router, that purchase would be a waste of time.  Any help or comments would be greatly appreciated!