I'm trying to make an installation using Arduino and Processing (Minim) to trigger sound. So far I have a PIR sensor connected to Arduino detect motion - as an object is removed from a box the sound plays and stops when it is replaced. It is very simple but I now want to have four of these pieces with the option of them all playing at the same time. The sound is heard via head phones attached to my macbook but I need to understand how to have four sets of headphones seen by processing and what equipment I might need.

Many thanks,

Frank