Problem with Sonos, Plex and ASUS DSL-AC88U: alternative for NAT loopback?



Dear all!

I had Sonos and Plex working properly but bought a new router (ASUS DSL-AC88U) and with this one it does no longer work. My Plex is remotely accessible, I can browse my Plex library in the Plex app in Sonos, but I get the infamous: "Unable to play - the connection to Plex was lost" error.

My current setup is manual port forwarding to port 32400, I tried with UPnP on or off (no difference) and, following the other posts, I added also the local IP address of my PMS ( in the Custom server access URLs. There is no NAT loopback (hairpinning or whatsoever) option on the router config.

Is there any other way I could configure the router to make Plex and Sonos work? A manual route from the sonos speaker to the PMS? Anybody else struggling with ASUS routers? I did actually by an ASUS instead of e.g. Netgear, because I thought they were "better" :(
In worst case I would also not mind if the Plex Sonos app would use the remote connection instead of the local one...

thankful for any feedback!

cheers, jo