Hi 
I think as you mentioned, you need to set up an array for that. And it’s the same for puredata - if I remember correctly, you need to set up multiple subpatches using poly or something.
I thought node.js can be an easy way to do it, but on windows I tried sound-play, play-sound and audio-play and none of them worked out of the box. I mean, their idea is to use external commands like mplayer behind the scene - so maybe the easiest way is to trigger a system command (e.g., mplayer) from Processing to play the sound with exec() - like exec("mplayer sound.mp3"); - if you don’t have to control the player (e.g., stop the sound, toggle loop)