Just wanted to add this to the list, in case anyone is interested. If you have Chromecast devices, it is a no cost way to turn them into Smartthings controlled speakers.
I have just released my latest version of the Logitech Media Server (Squeezebox) Smartthings integration. It can send player level control to any player that LMS has installed, including Chromecast devices through the LMS Chromecast plugin. SInce LMS is still doing all the heavy lifting of controlling what is playing, and this simply sends the appropriate commands, if LMS knows about the player, you can set up the player in Smartthings, simply using the MAC id.
I personally use this with a Boom, PiCorePlayer on raspi3, SqueezePlay on Windows 10, Google Home, and Google Home mini.
All main player functions work, on, off, play, pause, mute, unmute, next and previous track. TTS is implemented via the speak(message) command, with voice choices. It works with Big Talker 2 as well.
Music content can be started via 3 presets, unique to each player. So, a LMS playlist, artist, album, or genre can be associated with a preset.
There is a smartapp to associate buttons with the presets for anywhere a button can be used, voice control, Action Tiles, routines, etc.
Command list for smartapp/Webcore integration is in the documentation.