The truth about Apple/iTunes volume control?

Hi - I've always understood it's best to use the maximum volume setting on your computer when playing back music, controlling the volume with the amplifier. That has always worked for my ears, but now I have a new source (a USB DAC) that appears to be getting overloaded by the maximum signal from my Macbook Pro running iTunes.

I'm wondering if it would be possible at this stage of Apple and iTunes' development to lower the volume without losing bits. There seem to be recent reports saying yes, and one forum member said worries about lossy digital volume control were a "myth," although others disagreed. Today, I was told that it's OK to lower the volume on the computer to its "native level," a setting in the middle, or close to it, that is the default level when you first turn it on. I've got a Macbook Pro that has an overall volume control I'm wondering about, in addition to the iTunes. Unfortunately, it seems to be remembering my previous settings, such that I don't know what this native level is.

So, does anybody have any definitive answers on this?