Yep, they are not WiFi headphones so you cannot play your music library to the Sonos Ace via the Sonos app like you do with other Sonos devices. Simply think of them as good build quality, comfortable, nice sounding, expensive blue-tooth headphones.

Personally, I have a local Plex server installed so I play my music library both locally and remotely to my Ace headphones via PlexAmp. 

When they support the Beam for sound swap it won’t solve my use case where I want to listen to movies via the Ace headphone WHILE my wife still listens to the movie soundtrack coming from the Beam.
i.e. We have different volume requirements.
Unfortunately, this functionality isn’t supported, it is either/or but not both. So for my situation moving forward I will continue to simply use the Ace cans as bluetooth headphones. 

Hope this helps.

Ross.

Thank you. Will look into the Plex. Does it use the Sonos Music Library (mine is all downloaded - mostly from CD’s - on a NAS) And do I use the Sonos App or some other interface?

Re: Sonos headpohnes. Nice but no thanks. I have a great pair of noise cancelling bluetooth headphones. I ask the question… am I going mad… or are they! Looks like someone at Sonos doesn’t understand their own USP

Yep, I have my music library stored on my Synology NAS and it is shared by both Sonos and Plex.
If you have a Plex pass then you can play your music to Sonos devices via the Plex or Plexamp app.
You can also add the Plex music service to Sonos and access Plex content from there as well if you prefer.
If you have Airplay capable Sonos devices then you can probably play to them via Plex (without a plex pass) using Airplay. I haven’t tried this but I am sure there are others here that can confirm this option works as well.

Ross.

Thats amazing that they haven't built the headphones to be a zone player. 

Unbelievable really.

Yes, truly unbelievable. The high price of these headphones would be bearable if they were actually “Sonos” headphones. I don’t doubt the quality but they are hedphones with a Sonos badge but not part of the Sonos system .

Ask yourself if the Ace was designed for the huge wireless headphone market, rather than limit to the relative tiny number of existing Sonos customers wanting to listen to their local library source using headphones?