My guess is that the +2 speakers over 7.1 would be either height or width speakers for the front. Either are just what they sound like, speakers that are place high above the main L/R or off to the side (11.1 would usually include both), however neither are discreet channels. Instead they are processed content from the front speakers to help give a larger soundfield. However, it could simply be a doubling of either the rear or side surrounds.
Without knowing exactly what you are looking at we can't give you a specific answer.