I know that this is not exactly what you asked, but it might be a simple solution to your needs...
Plug in any set of speakers to the audio out on your TV (that ATV is connected to), and your TV effectively becomes the "Airplay receiver". The only catch is that you have to turn on your TV/ATV to work them.
This is the set-up I have and it's pretty cool. I use Airfoil to stream any audio (ie, Spotify) to my speakers!
i actually have this set up in my bedroom. this way, when i connect to the apple tv via airplay, it sends a signal to the soundbar and it turns on automatically, and starts playing music. literally all i have to do is connect to the apple tv from my device and push play.. the apple tv and soundbar does the rest.
i did want to update this with my solution i've decided on. due to finding this jailbreak gem called
Airfloat, i've turned my two old iPhone 4's and my ipad into airplay receivers. this, combined with airfoil, i have a total of 10 airplay receivers.
imac (airfoil)
2008 macbook pro (airfoil)
fiance's macbook pro (airfoil)
macbook air (airfoil)
1st iphone 4 (airfloat)
2nd iphone 4 (airfloat)
ipad 2 (airfloat)
iphone 5 (airfloat)
apple tv
airport express
i can finally give my fiance a reason for not selling our old apple devices
now i just need some more aux cords and decent computer speakers, and i'm good to go. granted, i'm no audiophile and neither are my friends, so as long as the speakers aren't fuzzy when the bass is up and it doesn't sound like they're coming from a netbook, they work. we have a
set of these dells at my work, and they fill our ~30x13 office quite nicely. i think i'll be purchasing a few of these in the near future.