@Leonardo since you can
lxc-attach you can log-into your Omnia box via SSH. Run
lxc-info <containername> while the container is running it should give you an IP (if it has one - not sure if it by default has a dhcp-client running). I’m assuming you can simply connect to that IP (Turris’ web-UI listens on default http port 80 I think). Alternatively - if you indeed use DHCP (as do 80% of router users) - you could also have a look at the dhcp-lease table in LuCi (the perspective of the Omnia on the IP-addresses handed out).
I think the guys from cz-nic have configured LXC as such that containers are normally automatically bridged (dealt with as if they are actual computers plugged-into the nework separately; i.e.get their own IP etc if you are using DHCP) to your network.
I haven’t run ‘Turris OS’ yet (virtually), but I assume it is the case when that template too to build an LXC container. But - as normally - a device has to be hooked onto the Omnia to run the initializing configuration setup, I am unsure…
P.S. I am not sure what the effect is of running router software behind a router (will it - by default - start dishing out IP’s too for instance? Make sure you are not creating a conflicting situation of any sort!
Keep us updated, and let us know how you solved it!