See message from Oct29 by Cat22 (me). Older firmware than in that message had similar results until I upgraded firmware to that shown. The firmware upgrade didn’t work and had to use tool and firmware file to get going.
What firmware you got and what app are you using IOS android? You’re describing 4stream so assume that’s what you’re using. Firmware is listed on 2nd “Speaker Info” page scroll down “Other Information” or use getStatusEx command on browser line to ip of each device.
Forgot to mention what your read in “manual” ain’t reality!
Also before going too far read topic “No Music When Link Rooms Together?” There’s some more tips and screen capture of app,
When you said you could play music on each, controlled via the app or remote?