I would recommend switching to minim library and using either AudioSample (up to 20 simultaneous overlapping voices)
http://code.compartmental.net/minim/audiosample_class_audiosample.html
or Sampler (customize your number of simultaneous voices)
http://code.compartmental.net/minim/sampler_class_sampler.html
For short sound effect playbacks that happen many times and may happen simultaneously, these classes are specifically designed for what you are trying to do.