I have seen plenty about Optical only being able to pass 2.0 but it seems the same goes for HDMI audio via the Audio Return Channel (ARC) system.
I am using the following devices:
TV: Sony KDL-55W905
AV Receiver: Onkyo TX-NR626
I have my XBOX One connected to my TV via HDMI 3, I have my TV connected to my AV Receiver via HDMI 1 going from the ARC supported HDMI 1 port on the TV to the ARC supported HDMI port on the AV Receiver.
With this configuration I am only getting PCM 2.0 audio passed to my AV Receiver. However if I connect my XBOX 360 to the same HDMI 3 port on the TV replacing the XBOX One I do get full 5.1 passed to the AV Receiver. This rules out the TV or the AV Receiver as being the root cause as the only thing changing is the audio source.
Just for clarification if I connect the XBOX One directly to my AV Receiver I do also get full 5.1, it's only when ARC is involved that it drops to 2.0.
(If anyone is wondering why I am not just using it through the receiver it's due to the XBOX One not correctly identifying itself as Full RGB colour space to the TV automatically, so I have to set the TV up for Full RGB manually and in doing so it causes issues with other video sources, so to get around it I am leaving everything else going through the receiver on HDMI 1 and just putting the XBOX One through HDMI3 directly which can be configured independently picture wise, however this lead me to discover the audio issue above)
Is this audio issue (and the Full RGB reporting) something that is being addressed?