Since it is xml in the source i think you have to use multimapping. for having filename in the target based on the number of records like 1,2,3, you need to use UDF/std function to generate the number and map it to target.at the end use variable substitution.
but this is going to have extra field on the target side.
else you have to use below approach to make use of DC.
A new approach: Multi-mapping Dynamic Configuration using a generic custom module