Sorry I'm late to this and you've obviously had your party.
You can check the settings in Apple TV to determine if you have the output set correctly. I'm sure this is well explained somewhere else, but...
It's possible there is nothing wrong with any of your devices. I suggest you Wikipedia surround sound and familiarize yourself with the formats and terminiology. Here's a crash course.
Blurays are encoded in full surrroung 5.1 or 7.1. 5 channels of directional audio (Front Left, Center, Front Right, Rear Left Rear Right) plus a Subwoofer (the .1).
DVDs can have 5.1 but often they are 2.0 or 2.1 meaning Left and right channel plus an optional sub.
I have no idea how you are connecting your TV.
Finally, to Apple TV and music.
Music is only stereo. Left and right channels. This is how all music is. It is how the source material is recorded and distributed. Only if you buy a music DVD will you ever get full surround. iTunes is stereo. Music on AppleTV is stereo.
Many movies on Apple TV are only stereo, even the HD movies! It is very misleading and one of my biggest frustration with Apple. The store used to say if it was 5.1, but now I believe they only show a Dolby Logo, but even that doesn't promise 5.1. It could be some compressed format such as Dolby Digital Plus.
Long story short, don't expect surround sound from anything on AppleTV and if you want that surround feeling, read the manual for your fancy sound system and change the input settings or surround settings on your AV reciever. Many have options to turn a stereo signal into a surrround automagically.
