You'll need a Z-Coupler or a resistor network at the BL-6000 end.

Here is some documentation.

2-pin DIN is always speaker level. It's easy enough to hide a Z-Coupler in an RCA plug. Measure the resistance of your "cable" from both ends first with the remote end open circuit, then shorted. If there is a Z-coupler in there, you'll be able to discover it.

I've forgotten the internal details of the BL-6000, but many of their speakers had printed circuit traces for built-in attenuaters. I would pop them open, remove a jumper and insert a pair of resistors.