Wow, really cool, and very interesting use of vocals in there . . . I wonder how much memory those samples took up. ;)
Oh, and on KungFuFurby's comment: good quality samples aren't related to CPU overhead (main CPU that is), since the Z80 is normally used for PCM playback (and often sound chip handling too). It's really a matter of good programming along with ROM space for good quality samples, that and well optimized 8-bit PCM samples in general. (PCM is limited to 26 kHz by the DAC in the YM2612, not by the CPU, and multi-channel 22~23 kHz PCM or DPCM is quite possible even with the Z80 handling the sound chips as well)
Key on any sample (preferably a looping one, as the noise will cut out early if you use non-looping samples), then make sure noise is enabled for the channel to output noise instead of the sample. Don't forget to set its frequency!
your gonna have to eventually upgrade to Mac OS High Sierra at some point. Snow Leopard has been out of Support for a long time now and Mozilla FireFox is no longer getting updates. you can't have Rosetta forever. Its time to find some new alternatives If that software doesn't work on Mac OS High Sierra. I will be upgrading my OS soon.