Hello
I dont know your stb, but some stb dont send the dd 5.1 sound over the hdmi! This is certainly the case for my Sky HD stb. For this stb I had to also connect its optical output to an sp-diff via a converter to my BS3.
Cheers
Peter
My B&O - BS3, BV4-50, Beomedia 1, BS3200, DVD1, BL8000, BL6000, BL3, BL2, BL7.4