One thought, which may or may not be helpful. 
 

Are you running multiple AirPlay 2 streams from your PC, or are you running a single stream and using the Sonos software to group the rooms together?

Hi Bruce,

I've tried it both ways I think, but I will try again as a test.

So I've got two Symfonisk speakers- both of which show up in iTunes, so if I stream just to one speaker, then Group, do you think that should work best. Well, any way I can try and see what works (or doesnt, as the case may be).

Before Sonos, I used to have the old Airplay plugs, which never worked well, streaming to one device only. But, I've never had a problem streaming music and video to an Apple TV unit, which has always worked well.

I do think that streaming to one speaker, and then grouping that one “room” with others should work best. My suspicion is that an AirPlay stream is wider bandwidth than a Sonos grouped stream, so if you use the Sonos system to group rooms, you’re taxing your WiFi signal less. 

Cool, I'll give it a go.

And it makes sense why grouping the one Symfonisk speaker to the two Play Ones nearest to the PC tends to work ok- less taxing on the WiFi signal.

And if I group the whole system together, what would you think would be the best "lead speaker" to group from. When I group for general whole house listening, I group with the Conect as lead, as that is plugged into the router. But for this it might seem best to start with the Symfonisk and add speakers to its group?

Honestly, I’ve no idea. Worth some experimentation. I’d start with the one “closest” to the router, under the assumption it has the strongest signal, but WiFi doesn’t always work that way, it seems. If you’ve got a wired setup, and the wired component is an AirPlay 2 receiver, I’d do that one for sure. 

Experimentation it is then!