Streaming music from ReadyNAS to an Android phone

I'd like to be able to access music stored on my ReadyNAS remotely on an Android phone. I had been assuming I would use Google Play Music through which you use their client to upload the music to their cloud and then play it in their app on the phone but it seems that the service has been discontinued since I last used it. I think I'm pretty flexible about a solution but the infrequency of use would preclude a paid-for service.The music is entirely in MP 3 format and the ReadyNAS is connected to the internet via a decent broadband service without usage limits so the solution doesn't necessarily need to involve cloud storage, I'm happy for it to be streamed directly from the NAS. A reliable and easy-to-use app on the phone is a must.

Thanks in anticipation...