I am planning my trip to Vienna September 25 through Sept 30, and looking for free musical events to see. Most musical events you can find online cost around 25 - 30 EU. So if you look up the individual churches, you can find their list of musical events. I notice that many (maybe most) of the musicians playing for this church are Asian - perhaps music students resident in Vienna? That's what I guess. So I will attend the Mendelssohn/Gounod concert with choir and organ on the evening of the 25th, if I can remain awake.
But please remember that a donation is requested to cover the church's costs.
While I was there a couple of weeks ago, I managed to catch two concerts: one at Ruprechtskirche and one at Mariahilfer. Both happened because I saw a sign while exploring the church earlier in the day, and returned later on for the concert. It's truly magnificent to hear this music in such beautiful and historic surroundings. A treat I'll always remember.
Not sure what the national origin of the musicians has to do with it. Vienna is a world hub for study in classical music. We are all citizens of the world.
On the music issue: I would suggest taking a tour of the Staatsoper given in seven languages. Es lohnt sich doch.