Hello,

  This is because the USB Audio Interfaces are external soundcards; they handle input and output via the same USB cable connection.

  Most users purchase an external USB audio interface because they're typically an improvement over the built-in soundcards of the laptops.

  Here's a document that covers this topic, and the photo in there illustrates the proper setup/behavior of our USB interface. Other manufacturer's USB audio interface follow the same behavior as well, so it's not a Line 6-thing per se.

  http://line6.com/community/docs/DOC-4156

  Regards,

  L6Perry