I'm trialing Spotify with a goal of using an old Android phone as a receiver. I want to taken an old Android phone with Spotify and connect it to an amplifier. I'd then like to use Spotify Connect with my other Android devices to playback music directly on this phone. This is OK, but often when I try to select playback on the old Android phone in Connect I can't select it - it says "Unavailable for Playback". It seems that I can only send music to it if the screen is on and Spotify is in the foreground. Obviously this isn't ideal as most of the time the screen will be off (it will be sitting there, connected to the amp). Is there a way around this to be able to play back to it all the time?