Hi, I don't use this model and I see no replies have been posted yet, but looking here http://www.samsunglfd.com/product/feature.do?modelCd=UD55A it looks to me like it's one SBB for each video wall then you loop each screen together using DVI in/out. As I understand it the screens split the signal resulting in a matrix without using a matrix processor. As I say I am not certain though.
Best bet if you are looking to purchase screens is to check with Samsung support before hand or your local supplier..
If you are in the UK, visit the website: http://www.dssceurope.com and Samsung Digital Signage support phone number is there.