65,000 is the absolute max.

Bluesound can index 200,000 +

Yes, it’s the total of all your libraries - quite a few users in the same position with their large libraries choose to go with Plex on Sonos. See this link:

https://support.sonos.com/en-us/services/plex

OK thank you so much for your fast response both of you! 

I suppose it depends how committed you are to Sonos. If the Bluesound kit genuinely indexes over 200k tracks it could be a better option, as Sonos have shown no interest in supporting larger local libraries.

As has been mentioned, Plex is an option. However, the Sonos version is very limited and is not much use in finding music - particularly if you have wide ranging tastes. The other Plex access mechanisms are more flexible - e.g. the web version. Worth a try, though - it may suit you.

The only way that I’ve found to handle these sorts of volumes is to run a media server on the Synology (I use the one called ‘Media Server’ :-)) and then use whichever access method you prefer. For example, I find that the Hifi Cast android app works well  when casting to a Chromecast audio capable device - either the now obsolete (but still available) Chromecast Audio plugged in to a Play 5, or directly using the CC capability on my AV amp. @Kumar of this parish has had success with other access methods.

Best of luck - and it will be interesting to know how you get on.

Thank you, amun. 

I see that the free version of Plex for sonos only play 1 min of the tracks found in collection :-/

I'm looking further to find a suitable solution continuing using my sonos system with my NAS. 

When I tried the Sonos version it seemed to play full tracks - the limitation was in how it displayed/sorted content.

Good to know, amun! 

I will try this, finally 

Thank you again! 

Plex has been installed on my NAS and a folder scanned & index.

Also installed Plex service on my Sonos and given access to my Plex account. 

I've given remote access in Plex parameters so Sonos was able to connect with the remote and indexed database.

But when I try to read a music file I receive a message saying "unable to read....file - connection with Plex has been lost"

I don't understand why this happens because the same file can be read without problem via the Sonos library... 

Try turning on UPnP on the router and see if that resolves the issue.

Indeed, it works with this change! 

Thank you very much for your help. 

Note: seems that my flac files are not supported by Flex…I'll finally make a selection of my best 65000 files and use the Sonos libraries for more flexibility and stability. 

I think .flac files are supported with Plex on Sonos, encoding upto 24-bit/48khz. So perhaps double-check that.