Hello and
The music for the film, as you probably know, was composed by Herbert Windt. There's also a number of older pieces included, composed by other composers (see the list
here). The music in the sequence you're interested in (I remember it well) was, as far as I could tell, composed by Windt (but I don't know whether he named it or not).
Cheers,
Ivan
Note: several posts dealing with the "Triumph of the Will" script have been split off into a
new topic.