I think this is dependent on the soundcard, if it has the ability to reroute its output to the internal input. But as you think you have done it before it should be possible.
I can only tell you how to do it with my soundcard (Terratec EWX 24/96) in Reaper:
Goto Options/Preferences/Audio/Device
select Audio system: Wave out
Input device: WaveRec Mixer (thats the option on my soundcard to capture the output, maybe look in the manual of your Soundcard)
Output device: Wave analog
Apart from that there are several programms to capture the audio from a video.
free and the most universal probably Super(C)
http://www.erightsoft.com/SUPER.html