Incorrect. AD or DA conversion incurs no perceptible delay.

Line-In (of any sort) requires a finite buffering delay, to allow for the variation in transit time across the network and prevent the playing device from running out of data.

@ratty So if i understand the sonos ray will not solve the lip sync issue since the optical cable come from the tv line-in.

The only solution should be hdmi arc connection with the sonos beam and sonos arc then?

If its the case, then sonos should provide an adapter to this because the beam and arc are expensive and at the end of the day i do not really need them.

The soundbars do not incur a perceptible delay because they are setup with an ad hoc one way 5 GHz connection to the surrounds/Sub.  This low latency connection is only reliable when all the devices are in the same room, because while fast, 5 GHz is not as penetrating as 2.4 GHz, which will go through walls/floors, but requires a buffer.  This is why rooms which are grouped with a TV source will also incur a delay. 

TV audio -- via a Ray/Beam/Arc/Amp -- is different from a general purpose Line-In.

As hinted above, a Line-In needs a 75ms (minimum) buffering delay, because the audio packets have to transit a general-purpose, shared local network. As such the packets can sometimes get delayed by other network usage.

TV audio on the other hand is handled locally, either within the Sonos unit connected to the TV or over a dedicated (not shared) 5GHz link to the surrounds/Sub. As such the delays are much more tightly controllable, so the lip-sync will be close enough not to matter.

Note however that if TV audio is sent to another, grouped, room then the Line-In buffering issues arise again, but only for those other rooms. In other words the grouped room/s is/are slightly behind (i.e. out of sync with) the Ray/Beam/Arc/Amp.

No, because all the home theatre units behave the same: Ray/Beam/Arc/Amp. It doesn’t matter how the audio gets to them. Delays are network-related, not as a result of the incoming audio format.

EDIT: @jgatie typed faster, but since I’d composed it here it is.

@ratty Then If all grouped rooms are wired ethernet cabled then i should not have the lip sync issue?

Makes no difference either way, Ethernet or wireless. The delays are as described above. Again, there should be no observable lip-sync issues for a Ray/Beam/etc wired to a TV.