Hi Alain,
No not like a phantom center channel, The processing is for steering the mix to a physcial 6th/7th speaker.
You can (I did early week with the 950 ....blushes) leave a non-existant speaker enabled, I heard diffrences - it will affect the recording, so in a sense it can be a diffrent PM choice, BUT was never intended to be used without the additional speakers.