Only Stereo Output from Roku, no Dolby Digital

I have a Roku Streaming Stick+ and I am not seeing it output Dolby Digital to my Sonos Playbar. My setup is as follows:
- Panasonic Plasma 50" HDTV (not used for audio, video only)
- Panasonic Blueray Player that has built in streaming capabilities, model DMP-BDT220
- Cable box = Google Fiber Set Top Box (STB) with HDMI out
- Roku Streaming Stick+
- Sonos Playbar w/ 2 Play:1 and a Sub that gives me the ability to listen to 5.1 surround sound.
- Monoprice or KanexPro HDMI Switchers (Monoprice MD-415ARC or KanexPro SW-HD4X1AUD4K)

In order to get the 3 different HDMI devices to connect to the TV and surround system, I am using a 4 port HDMI switcher with a Toslink output. The STB, Blueray player and Roku SS+ are all connected to the switcher inputs via HDMI, the TV is connected to the HDMI output and the Toslink interface on the switcher is connected to the Sonos Playbar. The reason I listed 2 switchers is because I was trying to see if the switcher was the issue and it wasn't. I am able to hide the equipment in a cabinet using a IR repeater with a Logitech Harmony remote and it works seamlessly.

However, when playing a video from Amazon Prime (that Amazon marks as being 5.1) via the streaming enabled Blueray player, the Sonos app tells me the Playbar is putting out DD 5.1 sound. When I play the same video using the Roku, I only see stereo. Are there options within the DD stream that would work with 1 device but not another?

BTW, I already raised the issue with Roku and while they said they were looking into it.

Thanks.