The transformer is from what i remember only there te reduce cable losses .
In this matter i would really wonder do you really need that .
I worked in a theater we had space for 500 people near the stage + 500 elsewhere .
We never used an 100 Volt system .
Unless you really have football stadium big places to provide with loudspeaker cables i wouldnt mind the transformer .
Ferrite isn't usefull for this transformer .
You really need a iron core for this .
For as far my memory serves me audio transformers are just like voltage transformers but then they transform resistance (except some winding differences ).
R1>R2 = N1>N2 (sorry for not being able to provide the correct formula's ,school is 20+ years ago