Yamaha has just released new firmware for it's 2013 range of Aventage Receivers. This means you can play all the music in the world to your theater receiver in decent quality.
It's pretty easy to do too! First update the firmware on your receiver, then simply make sure both the receiver and smart device are on the same network, open Spotify as usual, tap the play bar at the bottom and there should be a little green speaker. Press this and then select your theater receiver.
CX-A5000, RX-A730, RX-A830, RX-A1030, RX-A2030, RX-A3030, RX-V775WA, RX-V675