Just upgraded to Virgin Gig1 Fibre with Hub 4 from M200 Fibre Broadband).
Wanted to use Asus AX6100 (RT-AX92U 2 Pack) WiFi 6 System as mesh router to improve WiFi signal through house.
Hub 4 WiFi in router mode is better than Super Hub 3 in router mode but not great coverage in two storey house.
Got to say, it was a very smooth transition. No issues with DHCP mode for WAN on router, seems to be configured that way out of the box.
Switched Hub 4 from Router mode into Modem mode using 192.168.0.1 (changes to 192.168.100.1 for modem only access).
Connected AX92U unit with no problem, booting up modem first then Hub 4 connected using Cat 7 cable, then booted up first Asus unit (ground floor), then added second (first floor) via Asus Router configuration page http://router.asus.com
Changed network to previous SSID / password & all existing WiFi devices connected without issue then added Guest Network.
No issues, dowloaded Asus Router App for iPhone for monitoring & firmware updates.
Got to say Wi-Fi performance is superb 350 to 540 Mbps Download & 40 to 50 Mbps Upload throughout the house. Was getting this in same room as Hub 4 when in router mode but this decreased significantly in other areas of the house.
The second 5 GHz channel is dedicated to WiFi 6 (802.11 ax) backhaul channel between Asus units but you can use Ethernet cable instead.
I have no 801.11 ax devices yet to verify performance improvements on that band but will have soon.
Conclusion: Virgin Hub 4 & Asus AX6100 (2 Pack) mesh WiFi, a great combination.