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
for front and rear. The QuadDSP driver is meant to unify the
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.
https://git.inai.de/quad_dsp(clone only; no webview)