Best answer by John B
1. Having a Sonos device cabled to your router so that you are in 'Sonos mesh' aka 'wired' set up. This does nor necessarily have to be either of the amps.
2. A wired path between the two amps. That could be a direct cable between the two, or by wiring both to your router or to a switch. (Obviously, if you wire both to the network you have automatically fulfilled condition 1 as well).
See this link: