Could someone explain the differences between these two ingredients please?
Diastatic malt contains active enzymes.Non-diastatic has no active enzymesand is used for flavor (like molasses would be used).Bread dough needs enzymes.http://en.wikipedia.org/wiki/Malted_milkhttp://www.bakeinfo.co.nz/Facts/Bread/Bread-ingredients/Enzymeshttps://isbibbio.wikispaces.com/Fungal+Amylase+-+Baking+EnzymeCarl
Non-diastatic malt is simply for coloring and flavoring.
(The color change is most pronounced in the crust. You can easily go all the way from a light golden crust to a dark brown crust.)
Diastatic malt (often in the form of "malted barley flour") in addition to the coloring and flavoring effects also affects the developing chemistry of the dough.
(My own experience so far has been that with flour makers already adding "the right amount" of diastatic malt, it's overly tricky to do much better. My stash of malted barley flour sits in the back of my freezer and virtually never comes out:-)