Problem with Sony RDRHX 710 coaxial output

[Titansilver]

I have a new (a week old) Sony RDRHX 710 connected to a Philips DVD surround system (LX3950W) using the digital coaxial sockets.

The strange thing is that when I watch a dvd on the sony or when I watch a programme I've recorded on the hard drive it will play as 5.1 surround through the Philips. But when I watch a 'live' freeview programme on the sony it only plays in stereo with a loud hiss from the rear speakers. Any ideas on why this happens?

I can get 5.1 from live TV if I use the RCA connectors but then there is about a second's delay from when someone speaks to when the sound appears.