Q: Can I send audio from an Apple TV to multiple AirPlay speakers like I can with iTunes?
A: Unfortunately, not directly—this capability is still limited solely to iTunes running on a Mac or Windows PC.
Note that it is possible to work around this by using a Mac or PC running software such as Rogue Amoeba’s Airfoil. Although this would require you to leave a computer running, it would not necessarily need to be the computer hosting your primary iTunes library, and you would gain the advantage of being able to more effectively control the content directly from the Apple TV rather than having to rely on the iOS Remote app or directly accessing your computer.
Airfoil is a $25 app that allows you to stream any audio from a Mac or PC via AirPlay to multiple speakers. Combined with the included Airfoil Speakers app, you could stream audio from your Apple TV to your computer, and then use Airfoil on your computer to stream that audio back out to any number of other AirPlay destinations. You would simply select your computer as the AirPlay destination from your Apple TV, and then selecting Airfoil Speakers as the audio source on your Mac and choose multiple AirPlay or Airfoil destinations from there.
Airfoil Speakers can also act as a receiver on other computers, and free iOS and Android versions of Airfoil Speakers are also available to allow you to stream audio back to a mobile device, which could play that audio through a connected set of headphones or speakers. An Airfoil Remote app is also available for iOS that allows you to control Airfoil running on your Mac using your iPhone, iPad, or iPod touch.
Of course, since this requires you to leave a computer on with Airfoil running, it isn’t necessarily all that more practical than simply streaming from your iTunes library, but the ability to stream to other devices that aren’t otherwise AirPlay compatible—such as an iPhone or iPod touch—may be of some benefit, as is the ability to actually initiate and control playback directly from the Apple TV itself.