I've just upgraded my Superhub2 to the new Superhub3. I have an Apple Airport Extreme with a number of Airport Express devices. I happily had the Airport Extreme connected to the SuperHub 2 with the Airport Express devices increasing the WiFi range with no issues at all. As soon as I 'upgraded' to the SuperHub 3 all hell broke lose. This configuration simply does not work at all. The Airport Extreme will successfully connect to the SuperHub 3 for a short time, then start complaining that there's no DNS Servers and/or no internet connection. I've reset all the devices numerous times to no avail which has wasted loads of my time plus time spent talking with customer support. I only got it working by reverting to the SuperHub 2 which after many phone calls Virgin finally admitted there are issues with Apple gear. As it's under 14 days will Virgin refund me for the new Hub as I can't actually use it? Also when will this issue fixed and why didn't Virgin mention these issues when I enquired about it?
I Presume you are using the AirPort Extreme in Bridge Mode. One option is to put the AirPort Extreme into Router Mode, but unfortunately you would then have to put the Hub3 into Modem Mode and would lose its wireless. I have Hub3 modem mode, AirPort Extreme router mode and another AirPort Extreme in bridge mode. Everything works fine.
There are 10 types of people: those who understand binary and those who don't
I tried using the Modem mode on the SuperHub 3 and it didn't seem to work for me at all. When you connected the Airport Extreme to the SuperHub 3 what was your Airport Extreme Router Mode setting in the Network options? Did you select DHCP Only or DCHP and NAT?