This may sound like a really stupid question considering I've owned my Mac gear for almost 30 years but just what does the gain controls on my amp really do. Is it better to turn those up and the volume on the pre-amp down or vice-versa. I've always had them set at about 2 o'clock and never really thought about it.
Always leave the "gain" (volume) controls up as high as possible on the Macs. In other words, all the way up. Use the preamp to control the actual volume.
There was a thread about this a few months ago that explains the difference between the two. Gain vs. Volume