Hi @elite ,
If I have a DLNA receiver, in theory, STs commands should report from the speaker its connected to? yes, Of course you need to install your DLNA (Media Renderer) into smartThings.
Sorta like how Sonos would react to a door opening, or water in the basement? Yes,, You must have an app to select the events you want to send to speakers (ex media renderer events)
Would there be a way to get whatever I have running on the Roku through the receiver working on a DLNA receiver plugged into a cheap speaker? I dont think Roku is a Media Renderer, sorry I dont have a Roku.
Im not totally understand the music portion being controlled through STs - ST do not control your music, is not a DLNA controller for music, the commands are so limited and you can not list DLNA servers or other content, ST save all tracks you send to your speakers and list those track to send it like event , but is not a play list. you ned to send your music with some Controller like Tecnichs , denon or sony music remote (read the firs post of )