A bit of viola love: Max von Weinzierl's Nachtstück

Yes. It's originally for four violas! And you can download a PDF of the music here. The people playing are members of the Tertis Viola Ensemble, and are also members of the Munich Philharmonic.

As for Max von Weinzierl, I haven't been able to find out much about him. This seems to be his only published instrumental composition, but he clearly must have had a great deal of experience writing for strings (and, perhaps, playing the viola). I have seen reference to him as Max Ritter von Weizierl, which might connect him with this castle. He wrote a lot of vocal music, and might have spent some time in Salzburg (this piece is dedicated to a Salzburg druggist who was connected with the Mozarteum).