Apple TV4 has a problem decoding 5.1 audio (AAC, AC3 or pass thru). It will only output 2.1 channels no matter what I tried. I have used the original and latest firmware (9.0.1 as of this writing) and two separate ATV4 units. All other three ATV3 I tested does not have this particular issue. I also tried changing the Surround Sound setting from ” Auto” to “Dolby Surround” on the ATV4 and then two receivers I tested (Yamaha and Denon) will then display that it is decoding DD5.1 instead of Stereo before the setting was changed, but still only 2.1 sound comes out from the 5.1 speakers. Streaming service like Netflix is also affected as well as Home Sharing videos on my iTunes video library.
Best,
Jose