hi there i have a sky box connected to my bv7mk3 and i use a optical to sp dif convertor, the MK3 has SPDIF on AV1,2,3 & 5.
let me know how you get on as i woudl like to know some of the same if you can use AV5 for stereo sound and HDMI video but SPDIF for Dolby so i can use link rooms and Dolby
Good Luck
edit: I have one of these for sky. (NOT EXACT ONE but looks the same and has same connections)
http://www.audiovisualonline.co.uk/dynamic/eshop_products.set/ref/615/digital-optical-to-digital-coaxial-converter/display.html
Beovision 7 MKIV (Blu Ray)
Beolab 9
Beolab 6000
Beo 4
Beocenter 9300
Apple TV
SKY HD
Optoma HD65 Projector
Lintronic TT455-RT-238
Beovision 3 MKII