Orbi (Router Mode) using as DHCP server

Thanks for your really helpful response and for getting my post moved to the right category - it is a rather complicated structure!

So, we do have things operating as two routers. Orbi was rather unstable early on (this was years ago), so I separated certain network items off to sit on the ISP supplied device (Ring Doorbell/security cameras/home alarm system) so they would not be interupted if/when Orbi had a meltdown and, the wife could hop onto the alternate WiFi whilst I rebooted everything. This might not be needed these days, since Orbi is much more stable.

I've always been reluctant to use the Orbi in AP mode as it reduces functionality and the Virgin router is, shall we say, lacking..but is necessary as it's a cable ISP. We use the Guest network, Circle, Access Control that are not available on the other router.

Both routers use their own IP range, Orbi 192.168.1.. and the Virgin router 192.168.0... so, I've always assumed they would be fine.

Having reviewed the links you shared, gaming works through Orbi (my son is surgically attached to the PS5), though, interestingly, when speed testing, I don't get the same network speeds on the PS5 when wired directly to Orbi than I do if we wire directly to the Virgin box (150-250mbps through Orbi (RBR not RBS), >800mbps on Virgin) - could this be a sign of an issue as a result of the use of two routers? It's the only thing that I can see, when wired, that is significantly slower on the Orbi, compared to what I'd expect (for example, my MacMini which is wired generally gets >800mbps). Ok, in the grand scheme of things, 250mbps is flying however you look at it, but it's puzzling why it's not closer to the max speed that other devices get.

Anyhow, thanks again and hopefully this all makes sense.

Cheers,