Need more info on what device you are trying to play to really answer the question " What to push on the remote??"
but,
I don't know about Onkyo AVR's. I use the MO 4Media app, when I select my AVR as the destination and hit play it wakes the AVR and the music plays. The other JRiver remotes should work that same. You can also use the HTPC as the destination. You would need to turn the AVR on first.