For some reason advertising Plex web as a player doesn’t show up in Plexamp on iOS for me (but it does show up in the main Plex app on the same device). Also the desktop Plexamp does not seem to have an option to work as a destination.
But, on an M1 Mac, there is a solution: If you just run the iOS plex app and advertise it as a player, it shows up no problem on Plexamp mobile.
Why would I want to do this? I have a Mac Mini media server (it’s my Plex server of course) and it’s also connected to my audio system. I’d like to be able to have it start playing music without having to remote in or attach it to my TV. In addition to my Plex setup I can remotely invoke scripts on the media server to start/stop internet radio stations and so forth.
