I'm personally familiar with ecasound, whose library functions are available to perl through the Audio::Ecasound module. I can't say whether its heavyweight nature (intended for multitrack recording/playback and signal processing) will allow it to serve your purposes or not, but it's worth familiarizing yourself with if you have any interest in working with sound. OTOH, perhaps some command-line MIDI player accessed through system() calls would meet your requirements for something lightweight and cross-platform usable. Good luck!