The problem is that Sonos doesn’t support DLNA, and makes no pretence to do so. You may be able to direct content to a Sonos player using a third party UPnP control point, but it’ll be decidedly hit and miss.

Thanks Ratty; questioning DLNA compatibility seems a little confusing to me, here it's just upnp.
I even think internet radio playlists are not DLNA compatible (mainly why I use Logitech Media Server actually).
Here, all mp3 radios pass seamlessly but just those encoded in AAC not. Weird!

DLNA is based around UPnP AV, which Sonos also makes no formal claims to support. In my experience some years ago when playing around with a couple of third party UPnP control points and UPnP media servers Sonos would sometimes work, sometimes not. 

By all means continue experimenting, but what you’re attempting is totally unsupported. 

Yes, you should be right.

That being said, whatever Sonos compatibility, so far I can only see one solution: activate transcoding / decoding in the UPnP / DLNA Bridge plug-in from LMS (thank you Philippe!). I just tried, it works well.

The extra CPU load in server does not look significant either.

Yeah, I moved from the Sonos app to LMS Material Skin months ago, due to Sonos’ lack of Chrome OS support.  There are issues with AAC for unknown reasons.  I generally use Qobuz and FLAC streaming, which works great.

My first experience with Sonos leaves the feeling of a kind of closed world.
Probably making them run in an open configuration would not be the best option, despite their excellent performance otherwise.