Under the old system, in order to play your own music, you had to build out a service/server that was really confusing and flaky and system hoggy. I tried a couple of times but finally gave up because it was just too much of a PIA.
Under this new system, you download a fairly light weight application, point it to your music (in my case a folder on my Google Driver) and after it scans, all my own music is a button away through the radio's really nice speakers - either radio, actually... the one in the bedroom or the one in the living room.
I just fired up the stupid phone app and clicked on My Music, found the album I bought the other day - which is actually on my computer across the room - and it started playing in the bedroom. Pain free and nice.