Many Linux applications are not designed or simply do not support output of more than 2 channels. For those who can do more than two channels over OSS are struck down by the ALSA OSS emulation, which only supports two channels. What the OSS emulation does is to register two independent device nodes /dev/dsp0 and /dev/adsp0 for front and rear. The QuadDSP driver is meant to unify the dsp and adsp devices and provide one "true 4-channel" device.

This Kernel module is useful because not every soundcard supports these features at the hardware level.