Thanks for all these interesting posts, I really appreciate.
I was about to implement @
vaguedetails solution with the airport express plugged into one of the phantoms on optical but i couldn't find a toslink cable somewhere near me (would have had to order one on the internet). Instead I read into @ragwo's post and wanted to test a UpnP configuration. I ended up finding a free trial of the Audirvana UpnP solution. Since this solution is also recommended by Devialet, I gave it a try and, wow, it's incredible: easy to set up and use, works fine with iTunes, Qobuz and Tidal, and the sound is fantastic (I was able to stream 24/192 with Qobuz studio), such a huge difference from the Dialog/Airport Express system! I can only recommend this solution!
Now, I'll only have to migrate my Phantoms from their old dedicated Devialet wifi network (set up for the Airport Express/Dialog initial configuration) to my general home wifi network and I'll be done. I'll guess I'll need to reset the Phantoms and reconfigure them for my primary wifi.