Disabling Airtime Fairness (SONOS Support Recommendation) RAX75

Hello,

Sonos was jumping between my wifi networks and now it won't connect at all to the Nighthawk router (hard wired through ethernet or otherwise).  Sonos said that disabling airtim fairness is necessary, but even following the instructions in the manual :

(http://www.downloads.netgear.com/files/GDC/RAX75/RAX75_UM_EN.pdf): 

4. Select ADVANCED > Advanced Setup > Wireless Settings. The Wireless Settings page displays. Manage Network Settings 83 User Manual Nighthawk AX8 8-Stream AX5700 WiFi Router 5. Scroll down below the WPS Settings section and select or clear the Enable AIRTIME FAIRNESS check box.

This option is NOT available.  Sonos says they're compatible with this router (contrary to some comments on here).  NOTE THAT I HAVE AN RAX75 (selected RAX80 because it wasn't an option above)

Any help is appreciated on the airtime disabling issue as well as Sonos.

Thanks!