get two mono channel from stereo line

Hi,

We have a beagleboard with one audio line-in and one audio line-out.
From
the documentation both are stereo line. Now we want to use four mono
audio
line for our system. two input from radio and microphone, two output
to
radio and speaker. We use ALSA and we would like to know how we can
achieve
this either by plugin or programming alsa.

Thank you for your help

Arif