I've been intrigued about dual centres for a long time but have never tried it. There is always an argument about using two speakers on the same channel out of concerns about lobing effects. To make a long story short, two speakers in-phase and symmetrically positioned on either side would produce a lobe at the central viewing axis.

If it sounds good to you that must mean your M2 speakers are far enough apart that you are not experiencing this lobing problem. Maybe you are onto something.

John