Synology DS920+ issues with Sonos.

Sonos was working fine with the Sonos Music Library pointing to a share on a Windows 2012 server.

Sonos could see a MediaMonkey shared library hosted as a service on a Windows 10 (and 11) PC.

Sonos could see a Window Media shared library hosted on a Windows 10 or 11 PC with media streaming enabled.

With a Synology DS920+ NAS added:

Sonos works with the Sonos Music Library pointing to a share on the Synology NAS, so at least I can play some of my music (my main collection is too big for the Sonos Music Library). I THINK I could do this without the NTMLv1 SMB1 hack below, but may be wrong.

Sonos cannot see the Media Server library on the Synology DS920+.

Sonos cannot see the Plex Media Server library on the Synology DS920+.

Other PCs on the network can see both the Media and Plex servers.

My Sony KDL-40W705C can see both the Media and Plex servers.

Sonos does not, however, see the Twonky Media Server on my aged Zyxel NSA310

Adding the Plex service to Sonos does not allow it to see the Plex server on the Synology DS920+.

What is the subtle tweak that is needed to make Sonos play with the Synology DS920+ media servers?

I have applied the Sonos-suggested tweaks enabling NTMLv1 and SMB1 on the Synology DS920+ to no avail.