Well, I don't own a BL7-1 or /2 -- but my BL3s connect nicely through a Powerlink to RCA adapter supplied by B&O, and I would be surprised if you couldn't use a similar one with these speakers. The only issue being that you want to be certain you get a stereo-connection.
I have separate channel wires now, with a Powerlink plug in one end and RCA in the other. You would want a Powerlink plug with two strands of wire going out, to separate R and L plugs.