Mede8er HDMI audio problem

[Arthur]

I have a Mede8er 500X with latest firmware (4.04), connected via HDMI-over-twin-Cat6 to an Integra AV amp and thence to TV and projector. The MultiChoice PVR and and other sat decoders (Ku) play HDMi over the system without a hitch, including at full 1080p (so there's enough bandwidth). However, when the Mede8er is connected it outputs video but no audio, even at the lowest HDMI settings. I've checked every cable and all is fine. Connecting the Mede8er directly to the TV with HDMI is fine (ie audio and video are normal), but it simply will not go across the HDMI-extender network, whereas all other devices do.

Anyone come across this problem, and more especially a solution? Any suggestions?