Have you given Google Play Music a try yet? It should be on your PRIV already. It's pretty good and free. I use it occasionally, but mainly use BlackPlayer, which has a free version and a premium version. PowerAmp is also a very popular app.
BlackPlayer: https://forums.androidcentral.com/e...arkooperativet.blackplayerfree&token=5NuzIORr
Poweramp trial: https://forums.androidcentral.com/e...ails?id=com.maxmpz.audioplayer&token=WcJLetGE