Try this...Originally Posted by ChrisBensch
Open volume control, where you see all of the volumes.
Click Options, then properties from the file menu
Select the Recording radio button
Make sure that Line-In is selected
Then the recording volume controls will show
Make sure that the check box under Line-in is selected.
Try adjusting the volume here to see if this is working.
This is the core windows volume control for line in.
If not, then somethine is overriding it, and you should look into it to find out how the unit is controlling volume. If this works, then i would set this to a volume that is to your liking. I hope this helps some.