Give this a try.
I have an amp that accepts high level (bare wires) and low-level RCA. I had it wired to the high level on my amp and worked great and then as an experiment, used the adapter above and plugged it into the low-level RCA, and sounds exactly the same.
It is cheap and worth a try.
One of the other members is going to use a voltmeter to test if the signal coming from the sub part of the B&O amp is actually high or low level.
That is what i am using(kicker brand)....and what i am telling you is that is the only way to connect to the kicker amp there are no speaker/bare wire connectors on my amp. You have to use that connector and it magically figures it out.