U will need to turn down the line in volume.

Go to:
Start
Control Panel
Sounds & Audio Devices
Audio "tab"
Sound Recording Volume

In there is a "line in" section, mine is set just under half way, but just muck about with it until it sounds ok.

Also in the Hi-Q recorders options section, click the "Auto Set" box so that it will automatically set the volume for u.

Hope that helps :;