Success, thanks to the expert QUINNICUS.

I received a reply from HUMAX that stated that my HUMAX HDR-2000T was not HDMI CEC Enabled so will not work with the Sony BRAVIA Sync function.

So I have purchased via Amazon, the LINDY HDMI F/M CEC Less Adapter. I have connected this adapter in line with the HDMI cable from the HUMAX box to the TV HDMI socket (4).

Also connected to the TV are:

  - Sony BLU-RAY/DVD Player [HDMI socket] to the TV HDMI Socket (3),

 - Sony Soundbase HT-XT1 [HDMI OUT] to the TV HDMI Socket (2) which has the ARC function.

I am now able to utilise the Sony BRAVIA Sync / ARC functionality regardless of the state of the HUMAX PVR. The only problem left is the HUMAX volume control no longer works. A small price to pay for the convenience of having control via the TV Remote, of the volume of the HT-XT1, and being able to switch off (into Standby) the HT-XT1 when you place the TV into standby. Also the Sony BLU-RAY Player now takes control and switches the TV HDMI input to itself when you place a disc into it. After you finish with the Player, the TV reverts back to the previous HDMI selection.

I am also able to place the HUMAX box into its 'None Power Saving Mode' so I can feed through the Aerial antenna signal to use on the TV.

There is only one hurdle left, that is to educate my wife into using this setup.

Thanks again to QUINNICUS.