How to connect a Sub

[Mariner]

I have one question...
The manual of my C1sub (mk1) told me that, if I listen in stereo it is good to use two cables,
but if I listen in 5.1 I only should use one cable (line input).
My pre have two sub outputs ( with the same signal)
So should I pull out one of them when I change from stereo to 5.1?
Or should I only use one cable in general?
But t then is ask myself why ATC prefers two in stereo use.
Or didn't I got the manual wrong?
How did you connect it?

[ToddP]

When listening in 5.1, there is only one "sub" output, which is not really a subwoofer, but is called Low Frequency Effects (i.e. rumbles, blasts etc... but not usually music). When listening to music, the subwoofer outputs may have stereo content, so you should connect both sides to the C1 so nothing is missing. If your preamp is already summing the low frequency content to the sub outputs, there is no need to connect both.

[Mariner]

Thanks for your explanation!
So I will handle it like I did it in the past,
with only one connection. I was a little unsettled after reading the manual.