Hi,
first of all i have to explain my hardware setup: my surround receiver is rather old and only provides optical SPDIF. My HTPCs motherboard is rather new and doesn’t provide SPDIF 
So i’m using this HDMI splitter (sorry for the german link, but i didn’t find any english information) which encouples the audio signal from HDMI and provides an SPDIF output which is connected to my surround receiver. My TV is connected via HDMI to the output port of the splitter. The splitter provides two modi: using the sound settings from the TV, or allow passthrough the source signal. I’m using the 2nd option. With this option both VDR with softhddevice provides 5.1 sound and also with Kodi 16 i had no issues with 5.1 sound.
Now my issue: i’m not able to get 5.1 sound with my newly installed Kodi 17 beta3 on Gentoo Linux. In “Settings” –> “System Settings” –> “Audio” i see two audio devices: “HDA NVidia: HDMI” and “HDA NVidia (PHL PHILIPS FTV on HDMI)”. If i choose the first one, i do not get any sound at all – neither system sound nor sound in a movie. If i choose the 2nd, i get sound – both system sound and sound in movies, but in movies only stereo 2.0. It is independend which speakers configuration i choose in the sound settings, i’ve tried 2.0 and 5.1. If i set “allow passthrough” in audio settings during a running movie, also nothing changes, only 2.0 sound 
Any idea how to solve this? Here is a debug log from starting Kodi. I just played a movie with a 5.1 DTS sound track and turned off and on “allow passthrough”.
Any help appreciated…cheers Louis