I posted a similar question some time back. This is what I remember learning about iTunes and volume control.
1) The latest versions of iTunes (10.7 and up) have dithered volume control. That means that it performs recalculations to compensate for data loss. So you could use it. But remember, you are losing data when you turn it down from max, especially when you turn it down a lot, and you may notice a loss in sound quality the lower you go.
2) Most people recommend leaving the volume slider at maximum, and using your preamp to adjust the volume.
3) Using the track-specific volume adjustment in the 'Get Info' window is not recommended. Nor are 'Sound Check' or 'Sound Enhancer' functions recommended.
Hope that answers your question...
