BBC HD - no sound during programmes

Anyone got a clue what is happening here:

Recently I stopped hearing sound through my cinema system on BBC HD during live or recorded programmes; it works fine during the station promo (the fancy flying logo bit) and it works when listened to through a normal telly in the second room. All other HD channels are fine.

I was able to get sound back by turning off Dolby Digital in the Optical Out menu on the Sky box; however presumably this will give me poorer sound.

Output from the Sky box goes into a Meridian G68 processor and then on to a set of Meridian DSP 5500s.

Is the BBC sending some strange sort of signal which breaks my processor's decoding?

 

I think I may have solved it ...

Turns out that someone had pulled the plug on one of my Meridian DSP front speakers, so I was getting neither left nor right - just the big centre speaker and the rears. The programmes I had been testing with on BBC seem to have had zero sound to centre or rear (which is a bit weird in itself) ...

Now I am wondering why these programmes had zero sound on the centre speaker. One was Silent Witness, for example. Most mixes do have a bit of sound in centre, don't they?

 

Although the DD signal was transmitted the Silent Witness audio mix seemed to me to be stereo only. So far the only program that I have noticed recently with a decent 5.1 mix is the Jules Holland program.

 

http://www.bbc.co.uk/cgi-perl/whatson/search/daylist.cgi?day=Today&service_id=2075


According to this it's a stereo broadcast. BBCHD isn't all 5.1 broadcasts.

 

All programmes seem to be 'Stereo' on the guide, regardless of what they are. A few weeks ago one of the programmes in the Proms season was in Mono until I switched to the 48Khz PCM Feed.