Thanks a lot for your answer - that clarified it very much!
Now I just created a .txt-file in the root of my server, named it .htaccess, and included only the line that you wrote. And now I have audio :-)
Now, the only thing still not working is the music track playing in the first 3 levels (the music in the last level starts to play as intended). This might be my fault, though; I've set 4-5 sounds to preload in the beginning of the first layout, and I guess this might clash with the streaming of the music?
Again: Thanks a bunch to the both of you. The game is just a silly little excuse for the actual message, which is in the fourth and final layout: That my wife and I are going to be parents. We then intend to make our parents play the game through (with us in the room). That's also why it's so easy, and borrows graphics :D
Apart from that, it's a great opportunity to learn Construct 2 - I really like this program!