Trouble opening soundcard in Stereo mode

To create a complex audio source I want to open my sound card in stereo converting the two channels to an complex version of the audio source.

However though my soundcard is capable of stereo recordings it only opens as an single channel devive.
This seems to be an Linux problem as other sound recording tools apear to have the same problem
I have also tried another (el verry cheapo) usb sound card running into the same problem.
Running Ubuntu 8.04 64bits, soundcard is Inter high defenition sound hardware is Lenovo X61s laptop.
Anyone familiar to this problem ?