The best way to accomplish your goal IMHO is to use an Apple TV in your second location to stream music to your AVR. You can then use the free remote app from Apple to control music and volume on an Iphone/iPod/iPad. This is what Apple has to say about it on their website: www.apple.com/appletv/
Your music. Your speakers.
The perfect duet.
You’ve got tons of music on your computer. But the best speakers in the house are part of your home theater system. Apple TV connects them without missing a beat. Your iTunes music library streams directly to Apple TV. So you can sit back, choose a tune, and enjoy the music.
