OK! Solved it! [myslef...]
If you want to convert multiple resources into one do this:
add x amout of ammoconverters
first one drains material 1, second material 2 and so on
all except for 1st have toQuantity set to 0
you need all the storages to have the requires to be operational on.
Then it works just like draining few resources to make one! Hope I helped anyone who had same problem!