To record from your sound card without the Stereo Mix/ Waveout mix, you can connect line-out of your cound card with line-in (or speakers out with mic in) using an audio cable (that has a 3.5mm mini-stereo male on both sides). Although this is not the best method. In many cases the quality deteriorates significantly when using it.

Another option is to buy a sound card that has a "Wave Out Mix" / "Stereo Mix" / "Record What you hear" or a similar option.
For example, some USB sound cards from Creative support Stereo Mix/Wave-Out Mix/What U Hear. Although if you use a laptop, you'll probably won't like to have an external sound card (at least this is the last option I would use).


See also Vendor specific solutions:
How to modify the installation package of SoundMax driver to enable the Stereo Mix option