Exactly, not looking for Bluetooth solution, but thanks anyway @FBnil.As far as I read it, s/he's not asking for advice on streaming audio to a bluetooth enabled device (a hi-fi in his case). S/he's asking to use it like a chromecast, as in to leave the Pandora wired into the hifi, and to stream audio to it from their phone using something called plex. I don't know anything about plex personally so I can't really advise, but it seems to be a different situation as to using bluetooth headphones.
Debian ARM has a mini DLNA server, so a Pyra will work. (psst, buy a Pyra)Plex is a dlna server.