I've two echo dots, and I'm able to control them from the spotify app on my phone. I've the two spotify apps on my duet, but I'm not able to control the duet in the same way. Is there any way that I can set it up that the duet is another device like my echo dots? (or even what app would people recommend using controlling spotify on a duet via a tablet?)

(also just while I'm asking, I've one dot set up to use the line-in on my boom, is it in any way harmful to leave it plugged in and on like that 24/7?)