The AC12 is a ‘dumb` unit so there will be no configuration from M config. As such it can only be used in pairs as ‘M` always have done with digital theatre, i.e a left and right pair or a centre / sub config.
Dimensions are to be as follows: 120 x 40 x 30mm

That means, the AC12 is either by the 861 and you can use the (installed) cables,
and I can use it theoretical for each DSP ONE AC12- if I want.
Does the AC12 have ONE RJ45 in, ONE SPDIF out, ONE com in and ONE com out?
Do you have a picture?
In which price area is the AC12?
Thanks
Robert