Try Iori's SPU, it's quite good, but you have to configure properly the sound and xa buffer. I shouldn't be hard, try 4 for sound buffer and 10 for xa buffer. Try other settings if you are having problems. Remember to enable irq spu hack inside the plugin configuration but disable it in the epsxe configuration.
If you are not patient, just select internal's spu that is good also and doesn't need configuration(enable irq spu hack in the epsxe config.)