I suffer the same problem. 7 Sonos speakers of various types on the network via a boost (e.g. all speakers on sonosnet only). New flic hub can't find any of them, whether the hub is wired or wireless. the ios flic app picks them up fine in 'phone' mode.
I plan to try to give various configurations a go at some point but I don't really have the time for all that at the moment. Hoped it would work out of the box.
It would be interesting to find out the sonos setup of anyone else having these problems. I get the impression from other posts that flic tested with one sonos speaker connected directly to the network. That's about as far away from my setup as you could get.