Enligt spec så ska den klara det; http://blog.xctechs.com/vlogs/?p=331
"HE-AAC (V1), AAC (16 to 320 Kbps), protected AAC (from iTunes Store), MP3 (16 to 320 Kbps), MP3 VBR, Audible (formats 2, 3, and 4), Apple Lossless, AIFF, and WAV; Dolby Digital 5.1 surround sound pass-through"
Kör min ATV3 i sovrummet bara så kan tyvärr inte testa själv.
edit: Det här hittade jag på en annan sida; "When Dolby Digital is set to auto, the Apple TV will play AAC stereo when the source video contains both Dolby Digital 5.1 and AAC stereo audio."
"The Apple TV can pass through 5.1 AC-3 to a receiver if you set up the file correctly. Apple has the full details in a knowledge base article, but basically you need to set up your mp4/m4v file with a stereo AAC as the default audio track, then put your AC-3 track after it, disabled. On the Apple TV, you need to enable it by turning on Dolby Digital Out in the Audio Settings."