Recording Problem

Audition doesn't control the signal routing in your computer.  It just records what your sound card or audio interface hands it.

This, I fear, is where your problem is coming from.  Under pressure from the RIAA, computer and software companies have been removing the ability to record "what u hear" or "stereo output" on your computer.

What you can try is to go to the Windows audio controls on your computer (right click on the little speaker icon at the bottom right of your screen).  Select "Recording Device"..If you can see "What U Hear" or Stereo output, select it.  If you don't see that option, right click on a blank white area of the Recording Devices screen and make sure that there are ticks in the :"Show disable and Show disconnected Devices" boxes.

However I have to say that there are very few versions of computer/Windows left that will give you this option.  The last Windows that usually had it was XP. 

If you do some Googling, there are various bits of software that get around the, the most common being "Virtual Audio Cable" which isn't free and can take some setting up but does the job.