Are you using the W9980 as the main router, as I am confused when you say both 2.4 and 5GHz, as the W9980 is only a 2.4G device?
That is the way to use it, there is no need for the HH6. Guest isolation only works if the W9980 is used as the main router.
Is it the guest SSID or the main SSID which needs boosting?
There are better options if you need more coverage, I would not even consider using the HH6 as an access point.
Agree WD9980 is dual band. Have WD9980 DHCP range set as 192.168.1.100 to 192.168.1.199. I use staitc IPs out of this range for certain things (printer, network back up etc.) and all works OK. I have tried setting HH6 to 192.168.1.200 without permanent success. Then tried setting as 192.168.1.199 and adding to Address Reservation on W9980 - again only limited success. Used 192.168.1.199 without address reservation - again only limited success. It appears that whatever I try sometimes it will work, sometimes it will not. Interestingly even when HH6 does not work (i.e. connects to PC via HH6 wifi but no internet access) the HH6 will, on occasions display the Client List of the WD9980 with their IPs so HH6 must be 'talking' to the WD9980 - wierd!
In reply to Keith I only wish to extend 2.4 and 5; not worried about Guest.
What about setting the IP address on the HH6 to below the DHCP range of the 9980?
On my W9970, all my static IP adresses are below 192.168.1.100.
As @licquorice has said, you should be able to use the HH6, but the better alternative would be to use a proper dual band wireless access point, if you must have the 5GHz band as well.
I haven't got a hub6 only a hub5, the hub6 seems to have some odd DHCP settings. Just for information, I use 192.168.1.254 as 9980 address with 100-199 as DHCP range and have the hub5 set as 253. Powerline adaptor set as 99 (although that is probably irrelevant as it is just the management address of the device)
After a rummage through attic found old HH5. Have set this up and it sort of works!!
Can access internet OK and if I click on Win 10 >Settings>Devices it lists all devices on home network. However, when first set up HH5 I could connect to Network drive where all photos, music etc are stored but now I cannot. The only device showing under Win 10 network is the pc that I am actually using (connected by wifi to HH5). Also cannot connect to network back up drive.
This is another reason why I gave up in the end and consigned the idea as well as the HH6 to the bin.
This unit is fundamentally flawed as attested to by the the dire reviews of the HH6 just about anywhere you can purchase one from. As the unit is so bad, with key settings locked out to the home user, and the constant restarting - it actually causes more problems than it solves. If you want a stress free setup - dump the HH6 in the garbage and get a proper router that you have FULL control over. I now have 2 Netgear routers - one Primary for 'front of house'and the secondary one at the rear connected via Cat 6 cable to each other. I can then use all the Gigabit ports for super fast inter-'house wired connections to NAS etc., and at the same time have the Smart TVs connected and the PC all via these fast ports. I then use the Wifi solely for the Apple devices and automation. Believe me - stress levels are back to normal levels now with anything BT not in my life.
Have now got both HH5 and HH6 working as WAPs. One of my problems was that a Win10 update had, for some reason, modified my Home Network settings In putting these right I also enabled IPv6 via Services.msc and a Regiistry change. Whether it is coincidence or not HH5 and HH6 now both work as expected and have house and garden wide wifi. Only minor niggle is that if I power off WAP (either HH5 or HH6) then on power up they take an age to reconnect to the TD-W9980. No idea why this is but once it has connected then everything appears stable. Hope I have not spoken too soon! Now it is just the pesky flashing purple light.....