For the DVD or Cd audio I'd probably not go via a wave at all or analogue!

For your business thats a different story!!!!

For cdaudio its better to extract it as cdaudio directly .. the base utility is cdparanioia et al. K3B front ends this all nicely if your intended source is a CD.

For DVD then their are equivalant tools to do this for DVD's including the video if you like but you can also just capture the audio direct to mp3

DRIP and DVD::RIP are the projects to check out for this

For analogue input from a tape or whatever, its pretty easy but confusing. You should be on a full dupex capable card AND the card driver must be full duplex. Often this isn't the case....
(its a real pain getting the nforce audio to work full duplex)

The kmixer app can be confusing as to what is the actual source....
It is possible but maybe its your soundcard driver.....
what soundcard is it and which driver ????