SRPSRP - I've checked direct with Dolby, who have said they would only expect you to be getting prologic at the amp if the spdif or HDMI audio set-up was not set to surround.
If you have a G5 and a BT uhd service, in your set-up, I would recommend that you do not connect the STB into the Matrix/amp via HDMI as you will loose your UHD quality picture as the AMP is not HDCP conformant (use you TVs info setting to check what is being received). Added to that if the matrix is not HDCP thyt will also that will prevent the UHD video getting through. Even if it is HDCP, some units will, by default, degrade output to the lowest connected device capability for instance if you have a UHD TV and an HD connected into it they will output HD.
Try this ; check your STB is set to surround on SPDIF. Connect the STB HDMI directly to the TV and connect the STB via SPDIF direct to the amp
my surround has never worked on any channels over several software versions, no idea why and I doubt BT support would be of any help