do I use it?
Date: 20 Aug 1994 00:00:01 EST

  In order to enable 4-channel audio, you must choose "4-channel mode"
  from the 'Options' menu of apanel or make a call in your program to
  ALsetparams(3A). See the man page for ALsetparams(3A) for more infor-
  mation.

  Enabling the 4-channel mode will cause the electrical char-
  acteristics of your audio connections to change: the headphone jack
  will become a second line-level output (like the normal line-level
  output). The mic input will become a second line-level input *if* you
  have 'line' selected as your input source. If you have the input
  source set to 'mic', then the mic input will continue to behave as a
  microphone input.

  Lastly, when your machine is in 4-channel mode, the input and output
  sample rates will be locked together. Thus, changing the input or
  output rate in this mode will affect the output or input rate,
  respectively.

  You may also run 4-channel applications when the audio system in in
  2-channel mode, and vice versa (2-channel applications work when the
  system is in 4-channel mode).