Multi-Controller/Room Audio Playing Out of Sync when Streaming via Sonos App (Any service)

I’ve got a setup with 6 Sonos Connect units in 6 different rooms each of which have an amp and speakers connected to them via optical output connection. All are wirelessly connected to each other with just one unit connected via ethernet to my home network for direct internet access. Which then relays that access via Sonos’ own wireless network between units. Max distance between any of the units is 20ft or less. Everything has always worked flawlessly when playing something in any one room using the Sonos S1 app and a streaming service. However whenever I try to group 2 or more rooms to play the same audio regardless of the streaming service all the rooms are out of sync by as little as half a second to as much as a second or more. How can I get the whole house to play the same music in unison and all synced up? Nothing in the app allows for delay adjustment when streaming. Only for using line-in which doesn't help me. Only thing I can think of is having to hard wire each unit and disable wifi on all units. 2 of which will be a real pain to wire with ethernet so really trying to avoid having to do this. Any suggestions?

Thanks in advance.