Silence a single channel then downmix

[sumawo13]

I was wondering if there was a way to silence the center channel of a 5.1ch DTS audio track, and then downmix to 2.0ch. I've tried reading the Sox documentation but I can't make sense of it.

[J_Darnley]

You don't need to silence the centre channel first, just don't use it in the remix effect (it should be channel no. 3)