Bubble UPnP or ArkMC, they both have almost the same features the wireless streaming of media from the servers (UPnP/DLNA compatible) or locally from the devices.
I'm on Spotify premium. Interestingly, it appears that if you have Spotify on your PC, you can access locally saved tracks and add them to a playlist, which actually syncs to your phone as well available for offline mode, even if the song itself isn't available ob Spotify.
I'm fine with the default player. I do have KMPlayer set as default though. Lol.