John:
Let's reframe the discussion just a bit. The so-called "volume knob" does not actually increase the volume -- it actually turns it down. At full rotation (maximum volume), the volume knob is simply passing along the signal as it enters the pre/pro from the source. Most preamps seem to be at "full gain" at roughly 12:00 on the dial, which means that the rest of the gain setting is largely irrelevant. It is actually better when the volume pot must be turned up to around 3:00 to yield the maximum volume setting, since this range gives you a wider, more discrete range in which to adjust the volume. It sounds like your NAD is simply set to use more of the rotation range of the "volume" knob.