Poweramp now has an experimental service provider API for 3rd party music services on their build 862+ beta version. Maybe you would like to see it and try to integrate your services with this software.
Hey! Thanks for coming to the Spotify Idea Exchange. We've been keeping an eye on this submission for an extended period of time, and it doesn't seem this will reach the votes necessary to put it forward for prioritization. As such, we're marking this case as closed. This includes any similar suggestions that are received.
If we do have any new information to share, rest assured we'll check back in here with a new status.