If you don't see Stereo Mix, either your soundcard doesn't support it, or you need updated drivers.
Again, registering is completely free so you have nothing to lose by registering, it just protects your name and score.
Some bugs exist that may never be fixed due to the way the chat designer has decided to implement their spam filters on chat (repeated lines of text or unacceptable words / phrases).
But please bear in mind that in some instances, you may have encountered the "filtering" bug mentioned above. : Lets you query the question / answer for being incorrect** There's also a bunch of random triggers for certain words or phrases and the bot will talk back to you.
See if you can find them More to add, when I can be bothered * Right click on the excel file here and save it to your computer (left click might work too, depends on your browser).
Note: in some cases you can have everything setup correctly but stereo mix still doesn't work.