It may be worth considering NORMALIZING the individual grids first.
This will have the effect of removing different
uses of the grading scale ( i.e., some people may use the full range,
some a narrow band, some the highs only etc.). After the grids have been
combined the analysis takes place straight away. Although all the grids
used for Consensus Analysis must be in the same directory, you can later
save this combination as a new and separate grid for Difference