The next step is to deactivate the amylase, this is achieved by increasing the temperature into the 80c range.
This all requires time to cool, so should be prepared at least one day in advance. It may also be refrigerated for several days. Typically an Aromastück addition of 10%, based on total flour %, is calculated into a formula.
Due to the preperation time and care involved, the Aromastück is a seldom practised method in todays world of commercial baking short cuts. The rewards in aroma and eating qualities are there though and for the craft baker or serious home breadhead it's all quite feasible.
I believe that most any grain variety can be used, I can recommend rye, wheat and spelt for sure. Flour can also be substituted for cracked grains.
Bjorn over at the BrotDoc, does a great job of demonstrating the Aromastück technique, his post is in English and German, there are also several excellent formulas to be found there, that employ the method.