You need a decoder, typically a Beosystem 1, 2 or 3.
If you do a search, there is quite a few discussions about how to pull this off best, especially if your rears are B&O speakers as well. You need a receiver with regulated line output so that you can control the volume of the speakers ..... also, you need to supply them with a control power so that they dwon't switch off automatically.
Cheers
JK
BS9000, BS2300, BC2, BL2500, BL3, Bl2, BS1, BV8, BC4, A8