I think it depends as much as anything on how the operating system handles the screens.
I know with my Mac I can either have the two screens (not sure how I would even get three going without perhaps another video card) either as two separate scenes on each screen, or as a single scene relayed on both screens.
First B&O (1976) was a Beogram 1500 ... latest (2011) change has been to couple the BL11 with the BL6Ks *sounds superb*