Double check your network path and read over the steps in this article:
https://support.sonos.com/s/article/78?language=en_US

Thanks for your post.

Pretty sure I’m not doing anything ‘wrong’ having read that link (and the links off it). It seems odd to me that I’ve got this working on one Synology NAS but not on the new one. The path and user ID are obviously different  but I think that’s all. Any other suggestions please? 

Sonos needs SMB1 to be active…

The file system the NAS uses for the internal drives shouldn’t be an issue, I’ve used several different ones.

The usual issue with this is getting the NAS to support SMB v1 for sharing, many make that difficult as it has security issues.

I decided I didn’t want SMB v1 enabled and built an inexpensive Raspberry Pi based NAS to SMB v1 gateway that works well.

https://stan-miller.livejournal.com/357.html

I’m with amun here….and especially if there was an update to the firmware on that Synology once you installed it. It’s frequent that these updates turn off SMBv1. You have to explicitly re-enable it. 

Using two different Synology NAS systems, one is using the new OS for Synology.  Both work fine with Sonos; both required me to allow SMB 1 in the settings, which are different on the two NAS systems.  The bigger challenge for me is that I keep Audio Books, not music, on both NAS in MP3 and M4B format and this makes access on Sonos OK, but not as obvious as it could be since the Sonos orientation is to tracks , albums and artists instead of chapters, books and authors - but at least I can access the audio.

Thanks for all your advice. Both my old Nas and my new one have SMB enabled so I don’t think that’s my problem either. The music plays ok with my Synology music App (DS Audio) but just can’t get it to work with My Sonos. Very frustrating.

“have SMB enabled” doesn’t really define which version of SMB it is. It must be SMB v1, not just “any SMB” I know on my WD NAS, it required a very specific setting, which was detailed in this thread, but I suspect the settings on a Synology would be slightly different. 

Everything you’ve said so far, including the “it works with their app, just not Sonos” continues to point to an SMB issue. 

Now realise that on my NAS there are ‘advance settings’ behind SMB that show max and min SMB protocols of SMB3 and SMB2. There is the option to include SMB1 so I’ll try that when I get the chance and report back! Thanks again for your help.

Success!!

On my new NAS I have now expanded the SMB protocols to include SMB1 and music has been restored to my Sonos. Thank you so much for your help!