BDV-E870: surround sound not working?

[mcrowne]

When I run my BDV-E870 in setup mode with the microphone, audio appears from all six speakers, so connectivity is all working.

When I listen to any playback though, be it DVD/Blueray, Bravia TV or BT Vision box, I only get sound from the front left and right speakers, and no others.

I suspect some set-up parameter somewhere has become mis-set, but can't find anything that changes the situation.

Can anyone provide any suggestions?

Regards,

Mark