[Ilkka]

You don't have to disable the monitoring. You just have to turn down/mute the line-in input from the play control side. Just double click the speaker icon on the lower right corner of your desktop to access the sound settings. If you can't see the slider for the line-in, click options, properties, and tick the line-in. Now you should be able to turn it all the way down or mute it (doesn't matter which one). You shouldn't get any feedback after that.