2 Channel Audio Passthrough Not Working

[freakshow999]

Hi my system is Openelec installed exclusively on an Intel Nuc Broadwell I3, connected HDMI to a Pioneer VSX-90 7.1 traditional and 5.2.1 Atmos system with a Sony 4k display. CEC is turned off all a/v switching is done through the Pioneer.

I am not sure when it started but after upgrading to 6.01, and having a weird problem with the GUI sound volume being extremely low, I have discovered that both DD and DTS (both in all forms i.e. DTS-HD MA/HRA) passthrough for 2.0 is not working correctly and are being transcoded by the system. I have a lot of old movies on Blu-ray remuxes to .mkv that have 1.0 and 2.0 audio tracks.
In the case of DTS-HD passthrough works fine for 1.0, 5.1 and 7.1 tracks but all forms of audio are being transcoded when in a 2 channel format. I don't remember having the problem in the past. Because of the way my system is setup I never even use the onboard (KODI) volume control and actually had to connect a keyboard in order to turn my GUI sounds back up to an acceptable level.
Does anyone know of a fix?
Was there a Linux kernal update that may have caused this in the latest release?
I tried reverting back to 5.08 but that didn't work either. I didn't have this problem with my Chromeboxes in the past either.

[chewitt]

Enable advanced or expert mode in Kodi settings (which is new since 5.0.8) and re-check your pass-through audio settings.