Sonos S1 uses SMBv1 that Synology sees as a security risk, so they seem to be closing off ways to use this protocol. S2 uses more modern SMB versions.
I seem to remember Sonos uses another way to connect to a PC database. So you could try if a using a PC to store your music on would work in your case.
Rather than fighting your new NAS you could use an NAS to Sonos gateway that read a protocol your NAS was happy using and shared one (SMB v1) Sonos was happy reading.
About any computer that can run the SMB system will work, I tried it here with a Raspberry Pi Zero with excellent results.
SMB v1 Gateway https://stan-miller.livejournal.com/357.html
Open Media Vault has also been suggested and it is lech involved to set up.
Less technical solution for a Sonos Pi file server https://stan-miller.livejournal.com/940.html
Hey there! Thanks to folks for offering solutions to integrate my Synology NAS with my Sonos 1 system. I appreciate the workarounds, but for a non-network engineer like myself, they are a bit baroque. So I took the easy way out: I revived my old MyBookLive drive and remounted it. I was surprised that it allowed me to access it and re-setup its shares etc., and then allowed me to transfer my music files back to it. The Sonos Music Library is very happy with it, and I can play my tunes again. The only catch is--the drive really is on its way out. Its network mount on my Mac is tenuous and I now get lots of error messages when I try to access it via its web dashboard.
So, now to Plan C: There are some MyBookLive drives still out in the world, and I just bought one on Amazon. It’s refurbished, so I hope it works. I’ll be able to listen to some music till it arrives, at least.
If there are any Sonos support techs reading this, I’d like to say how much I appreciate your efforts in trying to make the Sonos 1-to-new-NAS-device work. The responsiveness of the Sonos live real-time troubleshooting cannot be overstated. (I also appreciate the efforts of the Synology techs, who tried to fix things from the opposite direction). However, I think maybe it’s now the best use of time and energy to tell Sonos 1 customers like me that, due to “progress” in the NAS protocols over the years, there is just no easy way to connect an old Sonos system to new NAS technology. I used up many hours of my time and Sonos tech support time (which is even more precious) coming to this conclusion.
Again, thanks to everyone for your suggestions!
Are you running SMB1 on the NAS?
Assuming you are, try this on the NAS.