My home is 2 stories, about 11 meters by 11 meters.
I have CAT6 cables running throughout.
1) cost most important
2) if wired, must work through a 1Gbps network switch. If wireless, must have decent range and/or work with 802.11n 100 Mbps (real bandwidth 72 Mbps)
3) simplicity (plug and play, or something like an autostart monitor-less Raspberry pi)
4) then reliability (will play most of day, every day)
5) audio quality least important. It doesn't have to be perfectly synchronized, as doors to rooms will be closed.