Connecting a subwoofer to the 440 Pro dual

[cescrig]

I want to add a subwoofer, specifically a B&W DB3D, via the RCA output.
I'm unsure how to configure the RCA output: as a pre-out or as a subwoofer output.
I want to set the subwoofer's crossover very low, at 40 Hz, using its filter, and I want the volume, once the subwoofer's gain is set, to be controlled by the Devialet.
I've tried to find the correct configuration, but haven't gotten a helpful answer. I'm hoping those of you with a subwoofer connected under the same circumstances can advise me.

[thumb5]

I have a similar configuration, and use the RCA configured as a sub-woofer output. I believe that's the recommended approach since it down-mixes the stereo signal to mono, which is generally what you want to drive a single sub.

[cescrig]

I have a similar configuration, and use the RCA configured as a sub-woofer output.  I believe that's the recommended approach since it down-mixes the stereo signal to mono, which is generally what you want to drive a single sub.

Thanks for replying.
Let me explain: The RCA port configuration would be:
Preamplified output (mono)
Mix mono
Relative level 0
Filtering Full range
Volume control Variable
And on the subwoofer, I'll choose the crossover frequency and other parameters.
Is this correct?