adding other speaker

At this time you can only add another Sub 4.  Adding more speakers than that, such as separate fronts, has been tested in Beta, but was found lacking reliability. 

Soundbars, regardless of manufacturer, comprise ultimate performance for convenience. 

However, you’ve tagged audio interruptions, and you shouldn’t be having that issue. Can you explain why that was tagged? You’ve also tagged the Sonos Five, which doesn’t appear in your post at all. Can you explain that issue as well?

r/sonos is more helpful if you want to read about other user’s experience with adding front surrounds.

https://www.reddit.com/r/sonos/search/?q=Front+surrounds&cId=df9c942a-c5ee-4233-a885-cb386c92d5ff&iId=8389a8bc-b3b8-4079-927e-d1e8b9d40fa9

Arc Ultra and Era-300s gives you a lot of Atmos channels, add in one or two Subs and it is rare to find different a system that has more or better Atmos performance.