Oh, nice. I put the two non-Airplay Sonos 1’s in my office, but I hate the Sonos app so much. I gave myself 30 minutes to see if I could do better and found AirConnect packages for my Synology:
I expected some futzing but it took more time to pick the right package than it did to get things working. Zero config except ticking a radio button during install. The stereo pair advertises itself normally and just works.