problems installing Netgear CAX30 modem/router

I recently tried replacing an older Netgear C7000v2 modem/router with a newer Netgear Nighthawk CAX30.   I was able to install and get access to the device from my laptop however the system reported a "bad" cable diagnostic report.  I was unable to get a internet service.  I called Netgear tech support and was told I had to purchase their Armor software in order for the equipment to properly connect.  I declined spending the extra money and replaced the equipment with my older gear.   I was also told that xfinity would soon not support DOCSIS 3.0 devices.   How can I upgrade my modem/router without having to go through this nonsense?   TIA