Client has 6 B&O speakers, all plug into wall, powered, all have RCA inputs. I am completely thinking line level in. Four in the family room run off line outs on an Integra AVR. BUT, two in his office (Beolab 6000) have real B&O cables with the 2 prong DIN connector on one end, thru the attic and down to an RCA plug at the speaker end. The amp end is adapted to speaker wires off Denon AVR speaker outs and operates normally. How can this work?

A line level input driven by speaker outputs will distort horribly, and you will only have about the first 20% of the volume control range on the receiver. Not so in this case. Does The B&O speaker have some sort of magical circuitry inside that senses a line level versus a speaker level?